The survey puts the Conservatives on 42 per cent (up six points on last month), Labour on 24 per cent (down one), the Liberal Democrats on 18 per cent (down one) and other parties on 16 per cent (down four, if still high).
The Tory surge will deal a further blow to Labour morale after a torrid spell for Gordon Brown which culminated in the party's heavy defeat in last week's Norwich North by-election.
Repeated at a general election, the results would give Mr Cameron a Commons majority of 152 and mean that many prominent Labour figures lose their parliamentary seats.
The increase in the Conservative lead from 11 to 18 points since last month suggests its strategy of stressing the need for spending cuts in the face of the economic crisis is chiming with the public. It is also a setback for Mr Brown's hopes of rebuilding Labour's popularity after seeing off a leadership coup and bringing in reforms to the Commons after the expenses scandal.
The party's support has been mired in the low to mid 20s for months, with only the slightest sign of recovery.
By contrast the Tories have achieved their highest level of support since April, indicating that they have recovered from the impact of the disclosure of some of their backbenchers' expenses claims. It is crucial for them to break through the 40-point mark to be on course for a convincing victory at a general election.
Backing for the Liberal Democrats remains broadly static, although the party will argue that it is a high base from which to mount a general election campaign, during the course of which its support tends to rise.
Reflecting widespread disillusionment for mainstream politicians, support for other parties remains high among the electorate. Their 16 per cent backing includes 8 per cent for the Green Party, 5 per cent for Ukip and 1 per cent for the British National Party.
Mr Brown's woes are underlined by the finding that just 59 per cent of voters who backed Labour at the last election still say they support the party. That compares with 94 per cent of previous Tory voters who say they intend to support Mr Cameron at the next election.
The Tory leader goes on holiday to France this week, leaving the shadow Chancellor George Osborne and the shadow Foreign Secretary William Hague to deputise for him.
The party plans a series of themed weeks – concentrating on such issues as crime, health and education – over the summer.
Senior shadow ministers are also working on a series of Green Papers designed to flesh out policies in the party's general election manifesto. They have been asked to identify spending areas where cash can be saved.
Despite the Tories' victory in Norwich North, the result carried some warning signs for the party.
Its share of the vote there, at less than 40 per cent, was read as evidence of a continuing lack of enthusiasm for the Tories despite the deep hostility to the Government.
Mr Cameron has admitted his party has yet to "seal the deal" with the electorate, and he wants to urgently deepen, as well as widen, Tory support.
Mr Brown, meanwhile, has also called for a flurry of government activity over the summer to counter accusations that his administration is drifting.
Although he is nominally on holiday in Scotland, he is in daily contact with Downing Street and has issued two press statements in the past two days.
His advisers hope that the Labour conference in September will enable him to get back on the front foot, although continuing dismal poll ratings could reignite mutterings against his leadership. For the moment, however, there is no sign of any appetite among demoralised Labour MPs for reopening the leadership issue.
The launch of Labour's much-trumpeted national plan, "Building Britain's Future", appears to have had little impact on the public.
Ministers are now pinning their hopes that glimmers of an end to the recession will enable them to argue that Mr Brown put in place the building-blocks of recovery and that the election of a Conservative government would threaten that. One cabinet minister told The Independent: "We have to keep banging away at that message. It is very hard going, but what's the alternative – give up and go home?"
Ministers also hope that the increasingly likelihood of a Tory victory in the election expected next May will increase scrutiny of opposition policies, allowing Labour to go on the attack against Mr Cameron.
ComRes interviewed 1,008 adults on 24-26 July. Data was weighted to be representative of all adults. Full details at www.comres.co.uk
How poll translates to election result
General election forecasts are made by applying the shifts in party support in opinion polls and applying them to the national political map. Today's ComRes survey suggests a swing of some 10.5 per cent from Labour to the Conservatives. Replicated nationally, that would produce a Parliament containing 401 Tories, 178 Labour MPs and 41 Liberal Democrats. David Cameron would preside over a majority of 152. Cabinet ministers Jack Straw, Alistair Darling and Ben Bradshaw would be among the Labour MPs given marching orders by the electorate.
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