Cameron under fire as candidate he imposed comes bottom of the poll

David Cameron is facing a backlash from sections of his party after the Tories failed to make progress in their first test at the ballot box since Gordon Brown became Prime Minister.

Labour held on to both Ealing Southall in London and Tony Blair's old Sedgefield seat - though with reduced majorities - putting a spring in the step of its MPs ahead of the long summer Parliamentary recess.

The results fuelled speculation that the Premier might seek to capitalise on a 'Brown bounce' in the polls and take a chance on an early General Election.

Senior Tories attacked the imposition in Southall of a candidate who joined the party only days before the poll and was beaten into third place by the Liberal Democrats.

Others voiced unease at the Tory leader's decision to rebrand the party 'David Cameron's Conservatives' in the constituency and about his wider strategy for taking on Mr Brown.

The Prime Minister is planning his first Downing Street press conference, and a major announcement on housing, for Monday, when Mr Cameron is on a trip to Rwanda.

Mr Cameron had put his personal authority on the line in the Ealing Southall poll, visiting the seat five times and having his name featured on ballot papers.

But the Tory campaign was rocked last weekend when it emerged that its candidate Tony Lit's company gave £4,800 to the Labour Party and he had been pictured shaking hands with Tony Blair.

A prominent backbencher has accused Tory HQ of treating voters with contempt by forcing the selection of the photogenic young businessman, and of seeking to exploit tensions between different ethnic minority groups in the constituency.

Former shadow minister Mark Field said: 'The centralised imposition of a Sikh candidate, who first became associated with the party ten days before the by-election was called and whose most recent political activity had been attendance at a Labour Party fundraiser in mid-June, always had the makings of a fiasco.

'Our consequent attempts to woo the Sikh vote in Southall by exploiting divisions which have wracked the local Sikh and Hindu communities for decades also struck many as blatant opportunism.'

Westminster MP Mr Field, in an article for the unofficial party website Conservative Home, pointed out that despite the 'frenetic and energetic PR campaign', the Tories' share of the vote had 'effectively flatlined' at 22.5 per cent since the last General Election - and this in a seat where in the 50 years to 1997 the Conservative share of the vote never dipped below 30 per cent.

Tory candidate Iain Dale, a member of the party's 'priority list' for the next election, said: 'Let's not pretend this was a satisfactory result. It patently was not. Questions will and should be asked about various aspects of the campaign.

'Although this is not natural Tory territory, most observers would reckon that in the middle of the third term of a Labour government the party ought to be able to increase its vote share by more than 0.9 per cent. 'We need to understand why this didn't happen.'

Shadow ministers have broader concerns about Mr Cameron's tactics for defeating Mr Brown at the next election.

While the Tory leader is widely considered to be coming out on top in their Commons jousts at Prime Minister's Questions, some senior figures doubt that his 'big idea' of standing for 'social responsibility' is resonating effectively with voters.

The Tory leader suffered another blow yesterday as close aide George Bridges - only recently put in charge of 'bomb-proofing' policy announcements in the wake of the recent row over grammar schools - resigned.

Friends said the decision had been taken well before yesterday's byelection disappointments, but will add to the sense of uncertainty about future direction.

Mr Cameron put a brave face yesterday on his party's showing, insisting its share of the vote had held firm in both by-elections.

He conceded: 'Obviously I would have liked to have done better.'

But Cabinet minister and Labour's election supremo Douglas Alexander said the results showed voters were moving 'back towards Labour'.

'If I was David Cameron, given his personal stake particularly in Ealing Southall, I would be deeply concerned,' he said.