I am old enough to remember decimalisation, which finally took place in Britain forty years ago this week. As an eleven-year-old in his first year at secondary school, who had never been abroad, it was my first taste of that slightly queasy feeling you get when you have to think in two different currencies at once. I recall the frisson as p’s and d’s mingled promiscuously in my pocket, the conversion tables on the walls of post offices and newsagents, the impending obsolescence of the eleven and twelve times tables.

But above all I am reminded of an event some ten years later: now a student at Birmingham University whose routes across the city often took in one of the alternative bookshops that nurtured the subculture. These institutions, defined negatively in that they offered what mainstream bookshops did not – a good coverage of left-wing politics, imported fiction and poetry, alternative health and non-western religion – nevertheless came to feel as if they obeyed a single organic principle.

They flourished in university towns, but not exclusively. As a teenager, I regularly visited a tiny one in Blackburn, Lancashire on my way home from school, spending money from a paper round on treats like How to Grow Your Own Marijuana, Henry Miller’s Tropic of Capricorn and the latest issues of Peace News.

Nowadays, that rapprochement is almost over, the trade fragmented between Buddhist Centres, herbalist emporia, welfare rights offices, with gentrified boutiques like the London Review Bookshop virtually the only places left for readers who think of themselves of independent mind. Where now can you walk in off the street and pick up a copy of Amilcar Cabral, Alexandra Kollontai or Ernest Mandel?

The nearest to my first flat in Birmingham was in Moseley, its volumes of Gramsci and Jung always faintly perfumed with jasmine and patchouli, although, with its squeaky wooden floors and gloomy mezzanine to the rear, retaining a studious air missing from its more activist-oriented twin situated on the curve of St Martins Circus Queensway in the city centre, filled with natural light that nurtured house plants and made hand-written cards curl around drawing pins on the noticeboard.

A mile away was the Communist Party bookshop, tucked away a block or two back from the busy A38, which pretty much stuck to printed material and felt a little more intimidating and austere in comparison, although it was already livened up with the snazzy covers of Martin Jacques’ Marxism Today and Robert Natkin’s colourful abstract paintings that adorned the cover of the first generation of Verso’s translations of French, German and Italian socialist intellectuals (most of whom are hardly spoken of today).

Not that these developments left much mark on Progressive Books and Asian Arts in Selly Oak. There were fans, incense, some fabrics and posters, but I was drawn to the shelves lined with the cream paperbacks of Peking’s Foreign Languages Press editions of Marx, Engels, Lenin, and of course Mao himself, alongside the darker hues of the rather more durable hardbacks that offered their Selected or Collected Works. A ramble on the web just now tells me that the bookshop was run in the 1970s by Jagmothan Joshi, General Secretary of the Indian Workers Association, a fact of which I was completely unaware at the time. When I used to visit, the proprietor was a taciturn and somewhat intense man in his late twenties or early thirties, perhaps an eternal postgraduate, whose longish hair, cardigan and brown suede shoes made me think of Karlheinz Stockhausen.

Not long after I discovered it, the shop was holding a closing-down sale, offering two-thirds off all stock. I chose The Poverty of Philosophy (60p, still pencilled on the now rather faded cover), Selected Letters of Marx and Engels (also 60p), Anti-Dühring (which seems to have disappeared from my collection) and a volume of Mao’s Selected Writings that included the Report on an Investigation of the Peasant Movement in Hunan and On Contradiction (£2). Even at marked prices they represented excellent value for money at a time when – as a glance at the back covers of other books I bought around the same time reveals – a copy of Discipline and Punish would have set me back £2.95 and Althusser’s For Marx a stomach-clenching £4.25.

And for each one, Stockhausen diligently calculated the promised discount. And what I liked about this ritual was, when he took up the Penguin edition of Engels’ Selected Works and noticed that the price printed on the back cover – for it must have been on the shelf for more than a decade – was an uncorrected 7 shillings and sixpence, without missing a beat he rapidly executed the mental arithmetic and informed me, with a hint of a smile, that I owed him 12½p.

I don’t know if this sale made the slightest difference to his fortunes as he made his way in the world following the shop’s demise. But in honouring the agreement to reduce his prices to the point at which they became almost meaningless I think he made a tiny difference to mine.