Gordon Brown has told the Independent today that he wants to see an anti-Tory alliance between Labour and the Liberal Democrats. Lord Mandelson said something similar on the Today programme yesterday. A Lab-Lib deal is suddenly all the rage – in Labour circles.

I'm as interested in a Lab-Lib deal as anyone else, but I don't think it's going to happen. Here's why. Labour has a secret in this election. They think they are going to lose. They think their only hope of retaining power is by some kind of deal with the Lib Dems. That's why they are suddenly agreeing with Nick all the time.

Look at the polls. In today's two new opinion polls Labour is third on 28% with Populus in the Times and third on 26% with YouGov for the daily Sun tracker. This is beginning to look like a pattern – and unless something significant happens in Thursday's debate, the pattern could become set in stone. Labour's interest in the Lib Dems, in other words, is the interest of the condemned man in a get out of jail free card.

Why should the Lib Dems give this the time of day? Search me. For 13 years, the Labour government in general, and in many respects Brown in particular, has been an implacable foe of co-operation with the Lib Dems. Brown can't even bring himself to call the Liberal Democrats by their real name; he calls them the Liberals, rather as some Tories always insist (or at least used to insist) on referring not to Labour but the Socialists. Any anti-Tory alliance proposed by Brown would be an opportunist alliance on his own terms.

In any case, and as the Guardian is reporting today, Labour is very divided, and always has been, about such co-operation. So what's in this approach for Nick Clegg? Not a lot that I can see. Lenin's remark about supporting the government as the rope supports the hanging man comes to mind here. But in reality, for the Lib Dems to support Labour would solve Labour's pressing survival problems while creating immense problems for the Lib Dems. Why bother?

There are, in fact, some reasons why there may be a window of opportunity for co-operation after 6 May that may not come again so starkly for a long time to come. A hung parliament on 7 May may be a big moment of opportunity for radical change in the electoral and political system. By the time of the next election things will look very different. But look at today's polls again. The Lib Dems are first on 34% in YouGov and second by a single point on 31% in Populus. Does that suggest anything?

To me it suggests that the increasingly real question is not whether the Lib Dems will support a Labour government after 6 May. It is whether Labour will support a Liberal Democrat government. Forget about the Lab-Lib deal, in other words, and start thinking about a Lib-Lab one. If I were Clegg I would sit tight and make Labour sweat. Brown is not really interested in co-operation. He is interested in clinging to power. And if there is one thing I am clear about amid the swirling currents of this election it is that the voters want Brown out, not Brown rescued.