And now, to add insult to injury, he must eat an expensive meal in the new five-star Marriott Hotel, while outside the windows, the terrace is prepared for a Peter Andre concert. The same terrace from which Ken once hung a banner carrying the latest unemployment figures will be capered on that very night by the one man in showbusiness most of us would fervently wish to see unemployed.
But if the weight of history was pressing heavily on the shoulders of the MP for Brent East, he wasn't letting on. "I'm just happy to be taken out for a free lunch in a nice restaurant," he said cheerily, as he waved aside my suggestion that we order a half-bottle of wine, saying he could easily manage an afternoon of paperwork after sharing a full bottle.
Meeting for a Friday lunch in the week after the hotel opened, Ken and I were the only customers in the grand, oak-panelled dining room, and therefore landed a plum table, with a view of the Houses of Parliament.
I'd worried that we would get the red-carpet treatment as soon as Ken was spotted, but none of the super-polite waiting team seemed to be British, so his presence initially passed unremarked. In fact, our waiter seemed bemused by Ken's absorbed perusal of the potted history of County Hall printed on the cover of the menu, and indulgently asked him if he'd like to keep it. "Yeees, I'm going to have a good chuckle at this," Ken replied mischievously, and the waiter went away, looking a bit concerned.
The lunch menu is surprisingly traditional, given that it was constructed in consultation with rising Irish super-chef Richard Corrigan. There's a bias towards club food, such as fillet of Scottish beef and grilled Dover sole, and a good selection of seafood, plus a few more eclectic dishes, including cold fennel and almond soup, to lure any politicians of the Granita persuasion.
Ken set about his starter of langoustine mayonnaise with gusto, dissecting his spiny victims with the doggedness and precision that have characterised his Blair-baiting mayoral campaign. My own grilled sardines came mounted on a slightly dry cake of apricot-studded tabouleh, and surrounded by a multi-coloured swirl of oils. "I have no objection to all that," said Ken, as he examined the effect.
Transgressing the unwritten code of restaurant reviewing, I inadvertently ordered the same main course as my guest, who has himself established an unexpected subsidiary career as a restaurant writer. But as it happened, Ken offered no opinion on our choice - corn-fed chicken with tagliolini and roast onions - other than to say: "I've stopped drinking my wine, so the food must be good." The chicken was milkily tender, and flavoured with fresh tarragon and nuggets of bacon, but I found the pasta over-salted, although I couldn't persuade Ken to agree.
In fact, for someone so flamboyantly definite in his political opinions, Ken proved frustratingly reticent as a reviewing companion. Peppering his conversation with put-downs of his opponents, who were either "ghastly" or "vile", he declined to engage in any detailed critique of the food.
When it came to our surroundings, too, he was non-committal, refusing to express disappointment at the fate of County Hall. I did, however, manage to provoke a certain amount of abuse from him about the aquarium downstairs. "Tacky ... a rip-off ... purely a tourist attraction," he fumedThe pudding list shows a more experimental bent than the rest of the menu - zanily so, in the case of dishes such as lemon rice pudding with tomato sorbet and basil sauce. My won ton with lemon curd, papaya and mango was a delicate layering of crisp pastry sheets, fruit and zabaglione, while Ken was blissfully happy with his white chocolate mousse. "I'm a white chocolate addict," he explained. "I wouldn't need to be tortured - they'd just have to dangle a bar of white chocolate in front of me and I'd tell them anything." Tony Blair's apparatchiks take note - the spectre of Livingstone as Mayor of London could evaporate with a judicious investment in the appropriate confectionery.
His afternoon of paperwork seemingly abandoned, Ken ordered a cognac, and I gamely kept pace with a Frangelico, a sticky Italian liqueur which tasted like a melted hazelnut choc-ice. In a final desperate attempt to prod him off the fence, I asked whether he would ever bring a guest to County Hall for lunch. "I don't know," he hedged, elusive to the last. "I'll see what the bill is." As it turned out, it was close to pounds 100, including our pounds 32 bottle of Pouilly Fume, but we discovered that it had quietly been settled by the Marriott's general manager, Michael O'Dwyer. Alerted to Ken's presence by the snapping of the photographer, he apologised for not having welcomed his historic guest earlier, and offered to show us around the rest of the hotel.
There followed a surreal - and from my point of view slightly blurry - tour of corridors and conference rooms. Into the Leader's Bar we trouped, to examine a framed photograph of Ken in a sailor's cap, then on through the Horace Cutler and Herbert Morrison suites, and into the humming, hi- tech business centre. "That's a coincidence - this is where the photocopier used to be," said Ken jovially. Even when told that a room in the hotel cost pounds 235 per night, he didn't bat an eyelid.
As we said our goodbyes on the terrace, surrounded by Peter Andre's amplifiers, a town crier appeared in full scarlet regalia, and he and Ken greeted each other warmly. The only surviving employee of the old GLC, the crier had been retained by County Hall's new owners to attract punters to the Aquarium, and he and Ken passed several minutes in happy reminiscence. He was the only person we met that day who didn't ask Ken whether it felt strange to be back. But I suspect he already knew the answer
The County Hall Restaurant, The London Marriott, County Hall, London SE1 (0171-902 8000). Breakfast 6.30am-10.30am (Mon-Fri); 7am-11am, (Sat & Sun). Lunch 12pm-3pm. Pre- theatre 3pm-6pm. Dinner 6pm-11pm (Mon-Sat); 6pm-10.30pm (Sun). All cards. Limited disabled access.