Ken Livingstone walks on to the Commons Terrace on a blazing afternoon, wearing dark glasses, a tieless shirt and jeans. He smiles wryly. "I've just had this ghastly woman on the phone from an American magazine who has spent the past 20 minutes trying to get me to say something nasty about Glenda [Jackson]. She gave up in the end. I haven't said anything nasty about Jeffrey Archer so I'm not about to slag Glenda off."
The House of Commons is in recess. Most MPs have disappeared for their holidays. But Livingstone is still beavering away. He has been reinvigorated by his campaign to be London mayor. Or, more accurately, his campaign to be allowed to stand in Labour's internal contest, in which the party's candidate will be selected. Since his election to the Commons in 1987 Livingstone has lacked a political role. After the abolition of the Greater London Council he remained famous for his appearances on TV but he has not run anything, not even a select committee. Now he has a purpose. "On my tombstone there will be one sentence: 'Abolished by Margaret Thatcher; revived by Tony Blair'," he says mischievously.
Livingstone knows that his revival could be extremely short-lived. While he is enthused by the prospect of becoming mayor, he fears that his renewed ambition could be snuffed out in the autumn. He insists he would remain in the Labour Party if the national executive stopped him throwing his hat into the mayoral ring. Obviously he has to say so in public or else he would give his political opponents in the party the killer ammunition they seek. But I believe him when he says he could not face leaving Labour in order to stand as an independent. Instead, he offers an intriguingly human response, rather than a political one, as to what would happen if his candidacy was blocked.
"I know exactly what would happen. I would go into a period of depression. I would get depression with associated psoriasis, a classic stress pattern.
"I've had very few depressions in my life, but they follow a pattern, and I look and feel awful for a few months. One such depression was in 1979, when I didn't get elected to the Commons. Another was in 1983, when the NEC barred me from standing in Brent East. The other was when we lost the election in 1992, when I thought, as many here did, that we would never win again."
So that is the most likely consequence of Livingstone being blocked: after an almighty row, the martyred Ken would sink into depression. He would not stand as an independent. In the meantime he is doing all he can to avoid the possibility of either depression or defection. He wants the party to allow him to stand and almost goes as far as to project himself as the new Labour candidate. He cannot actually bring himself to mouth the words "new Labour" but he does define himself as being "not old Labour".
He says: "My relationship with Tony Blair has never been anything but cordial. According to a Downing Street spokesman, he's quite sad that there's been this waste of talent over the past 15 years or so, when I haven't been allowed to run anything. He probably realises that I'm indelibly not old Labour. He and I are different kinds of post-old Labour, I suppose. We are part of the post-1968 generation. Before, it was about the big state machine making provision, in some cases tackling genuine evils. But our generation just became conscious of the bureaucracy which went with it. It's what turned so many people away from the welfare state, for example, and why the reforms have got to make it more of a service and less an instrument of social control."
At around the time the anonymous Downing Street spokesman spoke about the "waste" of Livingstone's talent, he himself made it clear, in an NS interview, that he was keen to serve in the government. He is still waiting. "Offer came there none. I think Tony assumed that, because I've been critical in the past, I would refuse to play the game of collective responsibility. That's not the case. If you are a minister you have pathways to influence; in return you have to be loyal to the government. I accept the trade-off. I would happily abide by rules of collective responsibility."
Would he be as loyal if he became mayor, when he would not be dependent in the same way on prime ministerial patronage? "There are one or two really big issues on which I would take a stand. If they proposed to break the trade union link, I would fight that. If they proposed a merger with the Lib Dems, I would oppose it, although that looks as if it's off the agenda now. But on all the other issues, where's the big difference? My views on public transport are in line with all the worriers in No 10 who say we mustn't be anti-car. I certainly don't think you should be anti-car, but you do need to hugely improve public transport." He goes on to make a detailed proposal. "Reluctantly I would use congestion charging. It would be £5 a day to drive into central London, a figure supported by many business leaders. I would freeze fares for four years, and then you've got to get the capacity up of buses and trains. You know, people remember the one time when London transport was getting better and I was running it."
Livingstone also promises to appoint a Blairite as his deputy. Earlier in the year he suggested that Trevor Phillips would be the ideal candidate, provoking preposterous allegations of racism from the Phillips camp. Now Livingstone makes a broader pledge. "A Blairite will be my deputy. You've got to have a balanced ticket. I am not daft. It would not be encouraging to voters if I appointed Linda Bellos [the left-wing former leader of Lambeth council] as my deputy. There are two blocks of opinion in the party and we win when we work together. Also, from a practical point of view, I would have to have someone saying: 'Look, Tony would like it if we did this or that.' But if I were mayor I would make sure I had lots of contact with the Prime Minister anyway."
So there you have a central plank of the embryonic Livingstone manifesto. But that doesn't impress his critics. Earlier this year the Home Office minister and former GLC councillor Paul Boateng wrote an article arguing that Livingstone had been an incompetent leader. "Just before that article I chatted to Paul about his GLC experience, and he said they were the happiest years of his life. Some ghastly thing from the bottom of the food chain decided on a change of strategy, that they were going on the offensive, showed him the article and told him to sign it. If you're part of collective responsibility, that's what you've got to do, I suppose."
But what about the normally mild- mannered Nick Raynsford, a likely mayoral candidate? In an NS interview, he complained that Livingstone had not attended any of his meetings with London MPs, in which he had outlined the details of the bill introducing the new mayor. Raynsford was the architect of the bill. "I'm a great believer that if you want to achieve something you put it in writing, rather than attend some ghastly meetings where everyone broadly makes the same point. When Raynsford published his white paper, my response was longer and more detailed than from any organisation. I also applied to be on the bill's committee. I was surprised that nobody ever sought my opinion directly as the leader of the last elected London authority, but I intervened with this massive document which cost me a couple of thousand pounds to put together and distribute."
Livingstone is a more complex politician than the "Red Ken" stereotype. He is a strong supporter of the single currency ("we should have joined at the beginning") and a critic of John Smith's vote-losing tax plans in the 1992 election. But he is well to the left of the Blairites and personifies a part of Labour's recent history that the modernisers view with horror. Yet they are by no means sure how to stop him. They may still persuade Frank Dobson to stand, and Tony Banks has some supporters. But Livingstone is right to assume that Blair has not decided whether he should be blocked in the autumn. Meanwhile, the great charmer expresses a provocative appreciation. "I owe a great debt of gratitude to our boss for creating a mayor. It has brought to the fore all the issues in politics which really interest me, from transport to regional government."
As we leave the Commons Terrace, an excited family approaches. They want him in a group photograph overlooking the Thames. Livingstone's continuing prominence is remarkable. He has been in no position of power since the mid-1980s yet is better known than most of the cabinet. Once the camera has clicked, I think of one more question. Does he still want a job in government? "Definitely. The ministerial ambition is still there. It would be just like Blair to block me from standing as mayor and then offer me a job in his government. Still, it might cure the psoriasis."