Peter York On Ads: Post Office speaks in a universal language. Does anyone understand it?

We're losing our shared culture. They were on about it on the 'Today' programme last week.

The idea is that there used to be a mass of common reference points that were resonant across the country, up and down the class system, across generations. This would help, say, the Queen Mother to talk to working-class women or Harold Macmillan to be a one-nation Tory communications wizard.

People who seemed to have nothing in common – life chances, health prospects, money – were at least able to make stilted conversation that would leave both parties feeling they'd connected across the divide. "Only connect."

Religion was hugely important here when practically all schools had God in the morning and a period of RE in the week. "Abide with me", "Jerusalem" and a mass of other hymns were hard-wired into the most irreligious young minds.

Meanwhile, the BBC – all of telly until 1955, all of radio till the 1960s – provided our home-made celebrities. Such impossible figures as Gilbert Harding or Sir Mortimer Wheeler were completely universal.

And there were other institutions – the Coal Board and the London Electricity Board – that supplied absolutely everyone. The universal phone book operated in a pre ex-directory world where Bermondsey and Belgravia numbers were listed side by side.

All this universality, along with its associated constraints and boredoms, and the fragmentation to come, is brilliantly described in David Kynaston's 'Austerity Britain'. It's an unimaginably different country.

But the Post Office is still there. Curiously structured, oddly managed – by high-profile, high-reward corporate outsiders – but still broadly public sector owned. Allegedly a mass of Spanish practices, the Post Office is a funny thing. How old do you have to be to feel warm and wet about it?

The new Post Office commercial presses every nostalgia button going. There they are, in a Victorian-windowed 'Open All Hours' cornershop set in what looks like a Northern terrace, with a proper cast-iron red postbox outside (inside, it looks more like a building society branch from the 1980s).

They've gone full-on with the casting. There's John Henshaw from 'The Royle Family' doing his usual; there's a nice Northern Mum, a perky young Asian assistant in a suit and a shiny-eyed Billy Budd apprentice. The script is tremendously Northern Camp in the Alan Bennett/Victoria Wood/ Coranora manner.

The manager has called a morning meeting because he's had an epiphany. "Are you all right now, Ken?" "Never better, Amir."

Then he sees the light – meaning the lovely traditional Post Office light outside, which prompts a very odd exchange in a mix of Blair-speak and marketing-speak: "That's not just a logo – we have more than a brand – we have an institution... we have the trust of the nation because we are the People's Post Office".

"Let's serve the people", says the shiny-eyed boy... "Let's serve Joan Collins." At that point Dame Joan enters to stage left for several seconds, greets Ken and does some minimal business before returning to Eaton Place or Cap Ferrat. She's just like the Queen Mother, providing the stuff of social cohesion.

I think it's very entertaining nonsense – but, with the exception of Joan Collins, I doubt whether anyone under 20 would recognise a word of it.