It is a single-decker now, equipped with CCTV cameras, and it lurches along its crooked route with a dispatch that unbalances even its most experienced passengers. In short, the evening bus from Oxford Street to Primrose Hill has become altogether less suitable for romance since the winter's night of 1975 when — as was revealed this week — Cherie Booth and Tony Blair fell into a breathless embrace in the back row.

Hilary Freeman, 36, a writer from Camden and a regular passenger on the 274, believes that it could now be dangerous to engage in any romantic activity between stops. “The drivers don't make it easy,” she said, clinging to a pole as the driver veered on to Prince Albert Road. “You get flung around. You would be risking life and limb.” She speaks as one with considerable experience in the art of canoodling on public transport. “I kissed on a Tube, a train and a bus. I was in my early twenties and I didn't care about what anyone else thought. I felt it was quite romantic, and at that age you don't have other places you can go. Blair lived in a shared house, didn't he? He probably didn't have any privacy at home.”

The future Prime Minister and his future wife were then pupil barristers. They had spent the evening dining in Soho with their boss, the future Lord Chancellor. Ms Booth wrote in her memoirs that they had ascended to an empty top deck, and when they got off, as it were, they “knew each other a lot better”. Ms Booth already had two boyfriends. By the end of this passionate ride, she had a third. Men were arriving in her life rather like buses.

Since that crucial encounter, the No 74 Routemaster bus on which they were travelling has been pushed out of public service and its route carved up between newer vehicles. It is the No 274 that now trundles the Georgian corridors between Oxford Street and Regent's Park Road. The back of that single-decker vehicle is the spot to which historians of modern politics must now make their pilgrimages.

Mrs Freeman, a regular passenger, believes that Mr Blair may be the only major public figure to have kissed there. “I haven't seen any other politicians making out on the 274 route,” she said. “Although, funnily enough, I once saw Gordon Brown snogging someone in a telephone box. It must have been in the early Nineties and I was queuing up to use the phone. It was in Covent Garden on Long Acre.”

Assuming that she was not mistaken, one can conclude that at least three of the main players in the new Labour project once engaged in bouts of romance in public places.

Though Ms Freeman was comfortable with whatever the future Prime Minister had got up to on her bus route, and thought a plaque of some sort might perhaps mark the location for posterity, other passengers preferred not to think about it.

“Terrible thing,” said an elderly gentleman as he disembarked. “Wish it had never happened.” A large drunk who was engaged in an abusive argument with the driver was dismissive of the historical significance of seats only a dozen rows behind him. “It's not f***ing interesting,” he told The Times. “Not at all. You need to get a life mate. These drivers are f***ing idiots. He's not telling me his driver number.”

“It's on the side of the bus,” said the driver as the drunk finally disembarked with one last volley of abuse. “I'm not having you on my bus again.”

Despite the loud ravings of drunks and the pitch and roll of the carriage, there are still young couples on the 274 keeping the spirit of Tony and Cherie alive. “I do see people kissing,” said the driver. “On Friday and Saturday night it's normal. It's not causing problems to anyone. It's nice.”

Times recommends

• A vicar’s wife: ‘There is no one to fight for us’
• Mutton dressed as lad: I’ve seen the future
• Think yourself slim with our hypnodiet podcast