Vince Cable is the Lib Dem that Tories love to hate.
A visceral cheer went up at the Conservative party conference when Boris Johnson predicted that the Tory candidate in Twickenham would unseat the business secretary from his south-west London constituency. He smiles: "Yes, I did take it as a compliment."
He doesn't complain about the brickbats thrown at him by the blues, and can't really for he has never been shy about dishing it out, variously comparing his coalition partners to the American Tea Party and Dickensian villains who sent little boys up chimneys. Cable always thought his party should present its relationship with the Conservatives as business-like rather than a love-in, which was the cause of tension with Nick Clegg during the early "rose garden" phase of the coalition. Those days are now long gone. As the coalition enters its last and increasingly quarrelsome chapter, no Lib Dem is happier to have a go at the Tories than Dr Cable.
"The working assumption" is that the coalition "will keep going" until next May, and he says his relations with the Tories on his departmental team remain "reasonably good", but the differences between the two parties are "becoming much more accentuated" as the election looms larger on the horizon. With relish, he lays into David Cameron for promising tax cuts to the Conservative conference, a pledge that pleased the Tory crowd while leaving many analysts wondering where the money to fund the pledge was supposed to come from.
"It's not just unfunded tax cuts, is it? They're [promising] dollops more money for the health service, soldiers, and various other things. You can't sustain fiscal credibility when you're offering at the same time massive tax cuts and other commitments, too. Two and two doesn't make seven."
Glad to beat the Tories with the stick they have often tried to wield against his party, Cable is enjoying himself: "This makes Nigel Farage look like a bastion of Gladstonian fiscal responsibility. When the dust settles, people will realise this is just not deliverable."
He's not much kinder about Labour. "They have two problems. One is the extreme vagueness about what their public finance policy actually is. It's all left very much up in the air. The other, the elephant in the room, is the last government and the way we finished up. There's the issue of believability."
So far he is being careful to stick to the script laid down by his leader. That is to bash both the Tories and Labour while leave the door open to joining either in another coalition. But there is much more of an edge to the way that the business secretary lays about the Conservatives. He becomes particularly angry at the mention of George Osborne's declaration that he wants a further big squeeze on welfare payments. "There's absolutely no way that making deep cuts in provision for the working poor is acceptable and that we can possibly go along with it."
So that would be a deal-breaker if another Tory-Lib Dem coalition was on the table? That would be a red line his party could not cross?
You sense that he would like to shout yes, but the approved script doesn't allow him to do so. "Well, I would, I think we're getting ahead of the game. We have no idea what's going to happen in the election. There's no point in anticipating discussions in June 2015. That's beyond my pay grade. But it's obvious that there is a very big gap between our positions on that and quite a lot of other issues. That's not something we would contemplate: massive additional cuts in public spending."
Speculating about who the Lib Dems might do a deal with in another hung parliament could turn out to be entirely academic if there is a huge cull of their representation in parliament. Their poll rating is flatlining in single figures and Ukip is now claiming the right to be called the third party of British politics. The Lib Dems have tried all sorts of strategies to revive their support and so far none appear to have worked. Yet, rather to the astonishment of some senior figures in other parties, Clegg appears completely safe in his job – at least until next May. Cable was forced to disown his friend Matthew Oakeshott when the Lib Dem peer attempted to trigger a challenge to Clegg in the wake of their hammering in the spring elections. "There's no leadership issue at all and I never was pushing for that," says the man always thought the most likely replacement for Clegg.
Cable agrees that his party's prospects look very bleak if you just look at their headline poll rating. "If you go by the averaging in the polls, obviously it's a nightmare. But there'll be a lot of seat-specific stuff going on. The Armageddon-type forecast I don't believe."
Some wonder whether Lib Dem prospects in leafier parts of London like his own might be hurt by the mansion tax, now copied by Labour and causing some concern among its MPs too. The author of the policy disputes this. "I've been out on the doorstep a lot over the summer. Nobody's mentioned it."
Not even people in £2m properties?
"I'm not canvassing the £2m properties at the moment. A lot of them are champagne socialists, Greg Dyke's road and so on. The high-income people I deal with on the doorsteps are much more concerned about things like the cost of childcare."
He hopes his conference speech on Monday will infuse his party with some confidence. "The key message – certainly what I want to get across – is that we've got an awful lot to be proud of. The theme will be very much what we've succeeded in doing in office, which is an awful lot more than is generally recognised." He lists industrial strategy – "got a big buy-in" – banking regulation, improvements to the minimum wage and tax cuts for low earners among the things that would never have happened had the Lib Dems not been in government. "We have made a really big difference … a massive contribution, things the Tories would just never have done on their own."
This is a message his party has been trying to broadcast for some time. Their dismal poll ratings suggest that the voters either don't believe it or aren't hearing it. He accepts that a significant chunk of their previous support felt betrayed when the Lib Dems got into bed with the Tories. "There is a segment of people who voted for us to keep the Tories out who have come to that conclusion. I meet a lot of them and they are angry people, some of them. I guess we must have lost them irrecoverably."
But he thinks his party shouldn't write off its chances of wooing back some of its former supporters. "I don't think it's quite as desperate as you imagine, because I'm meeting a lot of them on the doorstep. I remind them what I've been doing and they're: 'Yeah, yeah, of course we know. We think you're all right.' You take them through it and it's not as toxic as it was."
In Tory/Lib Dem marginals, he suggests that his party can still pick up tactical support from Labour voters. "Particularly after this week and where the Tories are now positioning themselves on Europe and human rights and tax and all that, if you are a Guardian-reading Labour supporter in Torbay or Wells or Twickenham, you know you're faced with a choice between the Lib Dems and some Tory. What are you going to do? You think these bastards sold out. I'm going to teach them a lesson. And have a Tory MP?"
Cable has had his bumpy, stormy and depressed moments in government, but like most Lib Dems he has enjoyed being the first of their kind to wield some power. He'd like to be in the cabinet for another term. "I've got a lot of work still to do," he says at one point. At another, he speaks of "unfinished business".
Whether he gets to complete it will soon be in the laps of the gods – also known as the voters.
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