As Gordon Brown returns to his Downing Street desk today the political prospect before him looks as grim as could be with one veteran Labour back bencher declaring that the Prime Minister is now "in the last chance saloon".

Austin Mitchell, who represents Great Grimsby and is often regarded as something of a maverick, becomes the first Labour back bencher, post-holiday, to launch a warning shot across the Prime Ministerial bow, claiming his party is "stumbling towards defeat".

In a website article for the leftwing Compass website, Mr Mitchell writes: "We already display too many of the symptoms of a government at the end of its tether: the bickering; the declining enthusiasm; the shuffling positioning and repositioning of leadership contenders along with escapist dreams about a period in opposition in order to get our heads straight."

He says that if all this builds up into a "death wish", it will not just be fatal for Labour but also for the economy, which needs rebalancing towards investment and production.

"It would signify a major step backward because, although the Conservatives haven't yet noticed, the national mood is moving back to favour regulation, public services and spending, state intervention and moving away from Thatcherism and failed market ideologies.

"This is why Gordon Brown, the prudent Presbyterian on his miserable British holiday in his respectable suit, is also in the last chance saloon."

The warning came as a poll found voters would overwhelmingly prefer to have David Cameron as Prime Pinister. The research by ICM for the Guardian put Labour 15% behind the Tories, on 29% to 44%, with the LibDems on 19%.

Mr Brown's personal ratings were even worse, with just 21% saying they would rather have him as Prime Minister than the Conservative leader - who was backed by 42%. Amidst the gloomy reading, there was one crumb of comfort for the PM, with Scotland preferring Mr Brown over his Tory rival.

Today, as he prepares to fly to Beijing for the closing ceremony of the Olympics on Saturday, the PM's mind will be full of thoughts about his autumn relaunch strategy.

Yesterday, part of it emerged with a highly personalised attack on Mr Cameron by Yvette Cooper, Chief Secretary to the Treasury, who decried "Cameronomics" as a mixture of contradictory policies and tax and spending plans that did not add up.

She accused him of using "frisbees, floral shorts and photo ops " to distract people from his "risky and destructive ideological agenda".

One major item in the Brown in-tray will be when to hold the Glenrothes by-election. Some reports have suggested that the PM could, as with Glasgow East, go short to get the expected political damage out of the way soon.

However, his keynote speech before the disgruntled trade unions is due on September 8, the Scottish Labour leadership result comes a few days later and the annual party conference in Manchester begins a week after that.

If there is talk of a leadership challenge early next month, a humiliating defeat at the polls could make the conference a potential bloodbath. A Cabinet reshuffle is on the cards and any momentum gained from that could be snuffed out by yet another electoral setback.

The rules state Labour has to call the by-election by December 4. The SNP holds its annual conference in mid-October, so Mr Brown would want to avoid giving the Nationalists a free campaign platform so near the ballot.

Thus, the window of opportunity closes with one possibility of holding the by- election at the start of November, taking a political hit but using a giveaway Pre Budget Report to seek to regain some political momentum.

However, there are many imponderables. If a leadership challenge does not emerge before the party conference in late September, then, after another by-election defeat in late October, will one emerge before Christmas?

One thing is for sure, this political season promises to be one of the most intriguing for some time with the overriding question being: will Mr Brown survive it?