The Conservatives have stretched their lead over Labour in the past month suggesting that David Davis’s decision to stand down as shadow home secretary has done no harm to their popularity.

The poll of nearly 1,800 people, carried out since Davis announced last week that he was forcing a by-election, puts David Cameron’s party on 47%, up 2% on last month, with Labour stuck on 25%, the Liberal Democrats still on 18% and others down two on 10%.

The 22-point Tory lead is the highest yet in a YouGov poll for The Sunday Times and compares with 20 points last month. Gordon Brown has suffered a record reverse since last summer when Labour enjoyed a 10-point advantage.

The Tory lead appears to be driven by deep pessimism about the economic situation. Asked what the state of the economy was, 49% said “quite bad” and 24% “very bad”.

Nobody thought the economy was “very good” and only 5% said it was “quite good”. For Brown, who has built his reputation on the economy, these are dismal readings. Nearly a third, 31%, think there will be a recession.

More than two-thirds, 68%, believe house prices in their area will fall over the next 12 months, although most expect the drop will be under 10% and that the downturn will be less prolonged than City fears that prices will not get back to last year’s levels until 2017.

Although people appear to be aware that high food and energy prices reflect international factors, a high proportion, 67%, blame Brown “a great deal” or “to some extent” for the economy’s problems.

Last week’s narrow Commons victory over 42 days’ detention for terrorist suspects has done little to boost Brown. Only 9% said the vote had strengthened him, while 45% said he was weakened.

Nevertheless, by 53% to 37%, most think Brown was right to press for an extension of the detention without charge period from 28 to 42 days.

Davis’s tactic of forcing a by-election on the issue is not backed. Only 29% think it was an act of principle.

One crumb of comfort for the prime minister is that the Conservative lead appears to be mainly a product of the government’s woes with the economy. Most are still insufficiently familiar with the Tories and their policies.

Only 32% say they know enough about what a Cameron-led government would do in power and only 40% think the Tories are ready for government. Surprisingly, only 35% think a Conservative government would handle Britain’s problems better than Labour.

Peter Kellner, president of YouGov, said: “Although Cameron’s personal rating is very high, these figures should sound a warning note. If the economy doesn’t slide into recession and oil prices come back down, there could be a significant Labour recovery.”

Following the death last weekend of the 100th British soldier in Afghanistan and further losses during the week, the poll asked whether British troops should stay. By 54% to 34%, people said the troops should be pulled out.

Finally, YouGov asked about the Lisbon treaty for reforming the European Union, following its rejection by Irish voters. Asked how they would vote in such a referendum, by more than two to one, 44% to 19%, voters said they would reject it.

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