Here's a message to ­Labour's wobbling MPs: grow a backbone. Watching them now, all a-panic as they contemplate their own political demise, some of them beginning to whisper about a leadership challenge to Gordon Brown, it's hard not to feel a surge of contempt. These are the folk who only seem to discover their spines when their own perks – or jobs – are in danger.

For years, most of them loyally trooped into the yes lobbies, voting for all kinds of horrors so long as the polls told them their seats were safe. But when Brown came after their expenses, they suddenly found the courage to say no. Now that they can see an electoral bloodbath looming, they're getting antsy again – and dumping all the blame on the man at the top.

All this would have a touch more credibility if these dissenters had cried havoc earlier, when something other than their own careers were on the line. Instead, Charles Clarke waits till now to announce that he is "ashamed" of being a Labour MP. As Ken Livingstone pointed out yesterday, that's odd coming from someone who faithfully stood by while the government made "all its worst decisions, including those that outstrip anything in the past couple of weeks, most obviously the war in Iraq". Of course, denying Gurkha veterans their full rights was wrong in every way. But it's hard to see why that prompts Clarke's shame when bombing and invading a country on wholly false grounds did not.

Labour is, as one MP put it to me ­yesterday, now divided into two clear camps: those who have given up all hope of winning the next election – and are therefore devoting all their energies to the "day after defeat, war-gaming ­various scenarios" – and those who still believe the situation is "retrievable". That MP is in the latter camp, though he admits it is getting "harder and harder" to persuade himself, let alone others, that defeat is avoidable.

I understand that sense of despair. For one thing, the starting assumption has to be that all incumbent parties, no matter how well led, are likely to be ejected from power given the current global slump. Nor do third-term governments tend to be re-elected: 1992 is the exception, not the rule.

Is is also true that Brown represents something novel in British politics. ­Normally the "electability" question hovers over opposition leaders: will the nation really choose this person as their prime minister? That proved to be Neil Kinnock's undoing in 1992. David Cameron has no such problem – not even his most bitter critics describe him as un­electable. Yet the question still ­lingers over the man who is already prime minister, installed in No 10 ­without winning an election in his own party, let alone the country.

These days Brown's allies don't bother to deny that when it comes to communication skills, emotional intelligence or the ability to convey empathy, he is simply lacking. Nor do they pretend that he looks good on TV or isn't cursed by some ­mysterious bad luck when it comes to imagery: how else to explain how he came to be photographed against a backdrop of swastikas when visiting a London school yesterday. They insist that it is substance, not smooth style, that will count come polling day. But that is an expression of hope: they will not be able to prove that Brown is electable until he has faced an election.

All of which makes the gloom understandable. But those itching to place the revolver at Brown's temple should hesitate. Some should ask themselves whether they weren't also agitating to get rid of Tony Blair not so long ago, so that Brown could replace him. The rest should recall that they failed to put up a candidate to stop Brown. If they feel they were so wrong two years ago, can they be sure they are right now?

What's more, the same problem persists: they don't have a candidate. They can while away the tearoom hours playing name games with Johnson, Harman et al, but all of them come with their own problems. A new face might bring a boost, but any gain would be offset by the image of a party first slaying its leader, then turning inward and fighting itself at a time of national economic ­crisis. Labour could surely not anoint a prime minister without a public mandate a second time – there would have to be an immediate general election. Do MPs really fancy their chances now, before even the slimmest green shoot is visible?

If, after it has weighed all that, the Labour party decides it wants to kill the king, then it should do so now, without delay. Otherwise, they should stand behind him. As one insider put it yesterday: "They should try rallying around him before they do him in."

For those at the top table, that means getting on TV, radio and into the papers making the case for the government they are meant to serve. Margaret Thatcher's cabinet used to do that for her, Blair's did it for him. Admittedly, it is yet another indictment of Brown that he does not have a praetorian guard of ministers ready to defend his every action (just as it is a sign of his weakness that Hazel Blears apparently has no fear of losing her job). But if Brown is such a weak communicator, then it falls to those more gifted to take up the slack. Ours is not meant to be a presidential system: the PM should not be a solo advocate.

Of course, that task will be made easier if there is a better story to tell – and this will have to be Brown's side of the bargain. He cannot hope Britons will re-elect him out of humble gratitude for steering them through a recession (if he does). He also has to offer a full programme for the next five years. Some of that is in place already – with a speech on education yesterday and one on crime, at long last, to come soon – but there needs to be more.

If he wants to win the loyalty, even the enthusiasm, of his party, a couple of bold strokes could work wonders: ditching ID cards and Trident renewal. He will also surely have to amend the part-privatisation plans for the Royal Mail, which Jon Cruddas describes as a "remnant left over from the last era", one that risks splitting the party down the middle. Ramming it through with Tory support could shatter any remaining backbench loyalty; abandoning it altogether could, who knows, trigger ­Peter Mandelson's third resignation – and the first on a matter of principle.

None of this will be easy. But if Labour MPs want to concentrate the mind, they should look beyond Westminster to the wider UK. This week sees the halfway mark for the nationalist minority government in Scotland. When I met the first minister, Alec Salmond, a few days ago he was in ebullient mood. "They're going down to a big, big defeat," he ­predicted for Labour at the next general election. Meanwhile, the polls show his Scottish National party riding high, on course to increase its majority at the next Holyrood elections in 2011.

That opens up a gloomy prospect for Labour. The assumed upside of devolution was that when one of the main parties was out of office in Westminster, they would rule elsewhere in the UK. But now it looks likely that Labour could be powerless almost everywhere: in Westminster, in Scotland and, given Boris Johnson's standing, in London too. Labour is facing a spell in the wilderness every bit as bleak as the long Conservative exile that began in 1997. To avoid that fate, Labour and its MPs need to get out – and start fighting for their lives.

freedland@theguardian.com