LABOUR'S 350-STRONG PARLIAMENTARY PARTY will return to the Commons tomorrow, but it won't be their usual Monday morning. Amid the serial calls for unity that have inevitably followed the party's massacre in last week's local elections in England and Wales, and the tipping-point victory of Boris Johnson in the London mayoral contest, many will be asking themselves: how bad does it have to get? More fully: how bad does it have to get before Brown is asked to go, offers to go, or is forced to go?

Which camp MPs fall into may define the potential civil war that Labour may endure over the remaining two years of Gordon Brown's premiership. For some of the party's most senior and experienced advisers, the panic after the worst showing in the polls for 40 years is a useless exercise. "Panic adds nothing. It's a way of believing you can act, when you can't act," said one aide. "What happened? Well, none of it is very complex. People are feeling the pinch on food, fuel. But global prices are out of our control. And there's our electoral cycle. People are now looking at the Tories and asking if they are fit to be the government, because the Conservatives are no longer toxic."

Others are less convinced and are asking a different range of questions with a far more serious list of options to consider. One London-based government minister described himself as "shell-shocked" after the electoral drubbing - which saw Labour fall into third place in the overall share of the national vote, one percentage point behind the Liberal Democrats (who took 24%), and a massive 24 percentage points behind David Cameron's rejuvenated Conservatives. He said he and many of his colleagues were in a "quandary". Admitting that no-one this weekend, or for months to come, will know the correct answers, the question remained about whether it was wise to change leaders now or wait.

He said: "If we have a new leader now, some believe it could mean we will lose the next election by a smaller amount than will happen under Gordon. Others predict a change of leader would fracture the party and we'd lose by more. And there are others still who believe that if get rid of Gordon now we could win the next election. Which is the correct option? Nobody knows."

For another MP, who accepts the leadership debate, however silent, has arrived and won't go away, there will be "no point in changing leaders if our policies remain the same." This advice, however, came with a political caveat and a warning to those on the left of the Parliamentary Labour Party who believe the pressure on Brown can bring about a return of old Labour values and old Labour solutions: "The type of social democracy that Tony Blair and Gordon Brown brought in with new Labour is with us to stay. A change of leader will not bring about a new political philosophy inside the Labour Party."

Despite there being no political calculator that can precisely turn local election results into general election seats, doom merchants inside the Labour Party were doing just these sums by Friday morning and predicting a Tory landslide in 2010 just marginally short of the 1997 majority of 179 won by Tony Blair. A handful of Cabinet members and more than 100 Labour MPs across the UK would lose their seats if the Tory momentum that saw Labour lose councillors and councils in territory once regarded as Labour strongholds, were repeated in a general election.

The victory of Boris Johnson as mayor of London, was for one former minister a triumph too far. "What was the name of the old man in the Magic Roundabout who used to cycle about the place? Mr McKendrick? Well, Boris Johnson as London's mayor is like Mr McKendrick winning the Tour de France. It shouldn't happen, but it f***ing has happened. So what are we going to do, dismiss it as mid-term blues, stick our collective heads in the sand and pray the Tories self-destruct? That's a long two years in the sand."

The comment was directed at Jack Straw, the justice secretary, who told the BBC yesterday that Labour could still win the next general election, adding: "They wanted to punish him Gordon Brown or punish us in respect of the 10p tax band."

Straw maintained that campaigning on doorsteps over the past month had left him understanding why people were angry with the government. "There's no question that the 10p tax has affected some people people are upset that a government which cared and continues to care very much about the low paid should be doing this. We're putting this right."

As part of the internal inquest over what happened in the May 1 polls and the urgent need to tell departing Labour voters that they will be listened to from now on, senior Cabinet figures were dispatched over the weekend to offer what one aide called a "listening and learning message".

After television appearances by Chief Secretary to the Treasury,Yvette Cooper, one of her fellow MPs described the performance as "a woeful script full of hesitant, repetitive stammering that contained only one message - we haven't a damn clue what the hell is happening to us'."

Others, even at ministerial level, aren't convinced the "listening" strategy is enough unless quick action follows. One said: "Will we listen to fears about increased immigration and be honest? We say the abolition of the 10p tax rate was a mistake, but will we put it back? We won't." Brown as a "listening prime minister" was also dismissed by another MP "as unlikely" because "Gordon's had a decade as chancellor and plenty of years in opposition. He does things his way. We get used to it, or we don't. The problem isn't just Gordon, it's the substance of what this government stands for."

Brown will attempt to address the substance issue in a policy offensive that is expected to start within a week. A draft outline of this year's Queen's Speech will be trailed in the hope that it will show the government still has ideas that are electorally attractive, vote-winning and innovative even after 11 years in power.

The focus will be on financial assistance for first-time homebuyers and other measures designed to aid those on low- and middle-ranking pay levels. One Labour insider said: "We made similar mistakes between 1990 and 1992. We forgot about aspiration. We can't afford to do so again."

What Brown and many senior ministers want most to do is to make it clear that Brown is the leader of the Labour Party, that his position is "unassailable". One senior aide said: "There is a new team in Number 10 under Stephen Carter. There will a raft of new policies that Gordon, for the first time, has fully shaped himself. And for those asking the question, does he have it in him to fight back?' the answer is yes, because Gordon Brown is not a sprinter, but a marathon runner. The panic should stop."

Except it won't. Some MPs back the assertion made by the left-wing MP Ian Gibson, that Brown has between now and the party's annual conference in Manchester in the autumn to demonstrate he can reverse the image that he is a lame duck PM.

One Blairite MP who has managed to thrive in Brown's premiership believes the party may yet find a self-survival instinct to dislodge Brown as PM.

"Gordon Brown has a sense of history unlike any other MP. He may yet be persuaded to go, if only not to repeat the failure of Jim Callaghan in 1979. I think Gordon Brown would rather be remembered as one of the great chancellors, rather than as a losing prime minister. He will know that if he loses, that will be the end of his leadership. He will also understand that if he stood aside, whoever took his place could lose and still be given more time. It would be a two-term job at least."

How bad does it all have to get? One Scottish MP, who said he wasn't looking forward to going back to Westminster tonight, said that was the wrong question. It should be: "It can't get worse than this, can it?"