I was born in 1985, two years after the pound coin was introduced and a year after the last pound note was issued, but it would be sixteen years before I'd put pound coins in my bottles. It's not that £1 was an enormous amount of money back then. It's just that my parents started with pennies. Every day without fail, from the day I was born, they would put a single one pence coin in a glass milk bottle. When the bottle was full, they started another one. On my second birthday they upped the ante: from then on, a two pence coin went in the bottle each day. On my fifth birthday, five. It wasn't until I was twelve and started a paper round that the denomination of coins I was saving started to increase faster than my age.

By then we'd started getting our milk from the supermarket, in plastic bottles that made for unsatisfying containers, so I was using jam jars, bottles of salad dressing, anything that had a neck wide enough to fit the 50p coin I put in each day, and was made of glass, so still made that satisfying clink.

I was too young to remember, but I like to imagine what it felt like in the aftermath of those seismic moments when we transitioned from one to two, from two to five, and from five to ten, as the rate at which we filled up milk bottles increased, then decreased, then increased again. Though by the time I was ten we must have already been using plastic milk. I don't remember.

Just over a month after my fifth birthday a new, smaller five pence coin was introduced. Perhaps my parents should have stopped there and then, taken the thirty or so old 5ps they'd collected to the bank, and had them replaced. But for whatever reason, they didn't. The old coins continued to be legal tender for another six months: I imagine a random succession of old and new coins dropping, one by one, into a milk bottle, the proportion of new coins gradually increasing, until some time before the 31st of December 1990 there were no old coins at all, and then, without my parents even realising it, the deadline came and went. So somewhere between one and six months' worth of my five pence coins are worthless metal.

A smaller version of the ten pence coin followed in 1992, and the fifty pence in 1997, but fortunately their dates of introduction fell three years before my tenth birthday and two days before my first paper round respectively. In 2001 I packed in my paper round and started a new job working Saturday shifts in a computer repair shop. I was now putting pound coins in my "milk bottle".

I don't know why I jumped straight from 10 to 50p when I started my paper round. I think I must have just been excited to have my own money for the first time. Whatever the reason, at age 12 I had skipped over the twenty pence coin completely. It would be almost a decade before I would come to realise the repercussions of that decision.

At age 18 it was time for me to leave home: that September I would start my degree in Computer Science at the University of Leeds. Before I went, I had another decision to make, one that weighed on me much more heavily, though it would ultimately prove far less consequential.

By this point I had collected eighteen coin-filled glass bottles and jars of various shapes and sizes, one for each year I had been alive. It wasn't, of course, a perfect mapping of one year to one container, 365 or 366 coins in each. It just so happened to have averaged out that way. I now needed to decide whether I would leave them at home or take them with me to university.

I agonised over this choice for much longer than it justified. I didn't plan to spend the coins but I liked having them around. They'd been constant companions ever since I could remember. There was something grounding about knowing I could look over to my bookshelf and see a milk bottle as old as I was, that contained a coin that had been put in it the day I was born, and a coin that had been put in it the day after that, and the day after that, and the day after that, in an unbroken chain leading right up to today. On the first day of term there would be 6,685 coins in those jars and bottles. University was, for me as for most students, a chance to reinvent myself, but they were one part of myself I was loath to leave behind.

In the end I did leave them behind, partly as a concession to practicality, partly out of a fear that the bottles and jars would be broken or the coins lost, spent, or stolen. As a leaving gift my parents bought me a large sturdy jar big enough, easily, to last me the whole length of my course. I don't think, really, that I needed to worry. Despite some wild times, that one big jar was never so much as scratched, and to my knowledge not a single coin went AWOL.

On the 25th of May 2005 I turned 20 years old. This was the first birthday I'd had since I was 10 where my age matched the denomination of a currently circulating coin, but I had long overtaken the 20 pence. Since I'd moved to university and got a better paying job I had begun saving a £2 coin each day, and as I'd jumped straight from 10 to 50p eight years ago there was not a single 20p coin anywhere in my collection at home or in my jar here in Leeds. I decided I would put one 20p coin in my jar, to mark my birthday, and then continue where I had left off with £2 coins the next day.

I made this decision lightly. It was months later before I began to regret it. In retrospect, I had no better option. I had set a trap for myself at 12 years old and now, eight years later, that trap had closed. That single twenty pence piece disrupted the perfect progression of 20 years of coins of monotonically increasing value, but without it, the sequence would have been incomplete. It gnawed at me, like, I imagine, a piece of grit does to an oyster.

There were times, in the year after my 20th birthday, when I came very close to giving up. If it couldn't be perfect, I wasn't sure there was any point in it at all. Sometimes I would dare myself to skip a day, or even stop altogether, but by the evening I would be sweating, and by ten to midnight I would panic, scour the flat for coins, and if I came up empty-handed, dash to the nearby 24-hour supermarket to break a note. There were more than a few nights like this over the course of the year, but despite these occasional outbursts of bluster and despair I did not miss one single coin. It was a hard lesson, learning to accept that I had made a mistake that could not and would never be undone.

That same year a competition was launched seeking new designs for the 1p, 2p, 5p, 10p, 20p and 50p coins. I didn't enter. I'm not a designer. But I did wonder what consequences the new coins would have for me. Fortunately, it turned out that the Royal Mint did not plan to withdraw the old coins from circulation, and they would remain legal tender. As I had now been saving £2 coins for a number of years, from the point of view of my collection it would be as if the new designs did not even exist.

The new coins were put into circulation in mid-2008. Barely more than half a year later, in a world reeling from the global financial crisis and the collapse of Lehman Brothers, Satoshi Nakamoto mined the first block of the newly created cryptocurrency named "Bitcoin". Embedded in it was this text: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks". Two years later, in 2011, I would be given 0.02BTC as a reward for signing up to a Usenet provider.

By 2011 I had been working as a software developer for the best part of five years. As I worked in tech, I was aware of Bitcoin, but it had never really piqued my interest. Now, though, the novelty of owning some prompted me to spend some time reading around the subject.

I should have loved Bitcoin. I immediately noticed the parallel between the cryptocurrency's "chain" and my own chain of coins. Individually, each block of the blockchain was worthless: it was only through their unbroken connection to Nakamoto's "genesis block" that their value arose. Similarly, my own genesis block, a single penny, loomed larger in my imagination than its monetary value ever could.

The value of the coins I saved each day had plateaued eight years ago and not risen since. There was no £3 or £4 coin, and the £5 coins issued to commemorate important events were impractical to save on a daily basis. They were also unsatisfying. As time went on, their rarity would confer on them, for collectors, a value in excess of their denomination. They were commodities, not currency, and I had no interest in this.

I had considered leaving coins behind in favour of notes, but the idea of tucking paper into glass each day seemed just as unsatisfying. So did increasing the number of coins I saved each day, from one £2 coin to two. "One coin - one day" had been the rule ever since I was born, and I liked knowing I could count how long I'd been alive using these little metal discs.

So I had stuck with £2 coins, and by now I had almost 3,000 of them. But their lack of upward progression continued to irk me, and, intrigued by Bitcoin, I thought seriously about the idea of a transition to it, either as a complement to my own chain of coins, or as a replacement. It would have been a wholesale change. There would have been no way for me to drop BTC into a bottle, except, I guess, on a USB stick. My chain would no longer have enumerated my days. In fact, all the reservations I had had with any of my previous ideas were just as true, if not more so, with Bitcoin.

I was tempted, nonetheless. My own chain, I had come to realise, was a solitary one. The idea of carting my coins to the bank and trading them in to merge them with a chain shared by millions of others held a certain appeal. I had sometimes felt cut off from the world and from people, and in the blockchain I saw the opportunity to link my life inextricably with theirs from the safety of my computer.

In the end I decided against it. The more I watched Bitcoin, the more it became clear to me that it had even less in common with a currency than did those commemorative £5 coins I had already dismissed. Its value was so volatile it would have been impossible to replicate the steady progression of my original chain of coins. Bitcoin was a tradable commodity, not money. I lost interest.

In 2015 I turned 30. There is, of course, no 30 pence coin, but the passing of another decade brought my thoughts inevitably to the 20 pence that marked the single frustrating exception to my otherwise unbroken run. 10,957 coins. Just one out of order.

In the year after my 20th birthday I had, as I have already said, felt despondent, deflated, on the verge of giving up. Now, ten years later, I felt much the same. Four years previously I had considered trading in all my coins for Bitcoin; I now considered trading them in just to be rid of them, for nothing much more than spending money. I didn't, of course. I don't know whether I ever could have. At some point in the past thirty years of my life there had been a point of no return, and I had passed it, oblivious.

Two years later, on the 28th of March 2017, a new £1 coin was introduced, a 12-edged coin in a bimetallic style that matched the two. This time, the old coins would not remain in circulation: motivating the change, said the Royal Mint, was the need to crack down on counterfeiting, to which, over the 34 years of its existence, the round, unimetallic pound coin had become increasingly susceptible. By some estimates a full 3% of such coins were now fake. So the old coin would stay in circulation alongside the new for 201 days, and then, at midnight on the 15th of October, cease to be legal tender.

This news brought up in me a complicated mix of emotions. I was reminded of my useless 5p coins, saved for me by my parents when I was too young to do so myself. I wondered how many £1 coins I had accumulated during my time working at the computer repair shop. My best guess, maybe 500 to 530. Most disconcertingly of all, I realised that I had not once considered the possibility that any of the coins I had amassed over all these years were counterfeit. I'd spent so long crushed by the thought of that twenty pence. It had never even occurred to me that it was almost certainly not the only blemish. This thought weighed heavily on me in the months that followed. I refused to face it head on. It felt like a scab which, if picked, would cause my whole self to crumble.

Somehow, though, as May followed April, and June followed May, the fog lifted. I found myself emerging into the summer sun with a newfound and unexpected sense of freedom, and a new relationship to my coins. It seemed paradoxical to me that a single, known flaw could have felt worse than an indeterminate number of others, but the knowledge that I could prove neither their presence nor their absence had, by some obscure unconscious process, eased my mind, and made me more accepting of my own error. Had I, aged 12, made a different decision, perfection might have been possible. I would never have known for sure. Now, 20 years later, I realised the torment I had avoided, and understood the calming power of the certainty of imperfection.

Which brings me, finally, to today. It's Saturday the 14th of October, 2017, 11:56pm. I'm sat on the floor of my spare room, glass of wine in hand, the bottles and jars that contain my 32 years and 11,830 coins arranged haphazardly around me. I'm here only to mark the pound coins' passing. There was never any question I'd dig them out and exchange them. Perhaps I would feel differently if I didn't know that, though the coins will cease to be legal tender, banks will, for some unspecified period, still accept them. But I really don't think so. The coins are no longer money to me. I will never spend them. Neither currency nor commodity, just my way of marking my age, and the slow accumulation of days.

The clock strikes midnight, and I raise my glass in a silent toast to the round pound coin, 21st April 1983 - 15th October 2017.