Voters have given this week's budget a cautious welcome despite plunging consumer confidence, according to a Guardian/ICM poll. It suggests most still tolerate the government's plan for spending cuts – or think they should go further.

The poll puts the Conservatives back into a narrow lead, although movement between the parties is within the margin of error. Tory support is 37%, up two, and Labour is 36%, down two. The Lib Dems are on 16%, down two on the last ICM poll. Other parties score 11%, up two, including the Greens on 2%.

Guardian/ICM poll

In recent polls from other firms using different methodology the Lib Dem rating is lower and Labour consequently higher, with the Tory score similar to that found by ICM.

Despite Saturday's protest march in London, public tolerance of cuts seems to be sustained. Only 35% think the plans go too far – a 10-point drop since ICM asked the question in November. Meanwhile 28% think the government has found the right balance and 29% say the cuts are not severe enough. That amounts to 57% support for current cuts or more.

The coalition is split: 43% of people who voted Lib Dem in 2010 think the cuts go too far, against 17% of Tories. Among current Labour supporters, 57% think the cuts too deep.

The wider verdict on the budget is mixed. People who think it will boost the economy outnumber those who think it will harm it by a net nine points. But most – 48% – expect it to make no difference. Only 50% of Conservatives and 23% of Lib Dems think the budget will strengthen the economy. Nigel Lawson, once famously branded Thatcher's "brilliant chancellor", says in today's Times he is "deeply concerned" about George Osborne's plan to merge income tax and national insurance, calling it "a huge elephant trap". "This superficially attractive reform was known in the Treasury in my time," he writes. "It became increasingly clear that what looked at first sight so elegant and logical was in practice a huge elephant trap and I aborted the project."

Osborne's fuel tax cut was a drop in the ocean. Only 21% think the measure was about right, while 4% say it goes too far and 70% say it does not go far enough. Supporters of all parties want more action to cut the cost of petrol.

It has also emerged that Osborne is considering offering hundreds of millions of pounds in tax breaks for gas companies, after the sector warned that a windfall tax on companies operating in the North Sea – designed to finance the cut in fuel – could strangle investment and push up prices. The background is a fall in economic confidence to levels only seen at the height of the financial crisis. Only 43% are now confident about their personal financial circumstances and ability to cope with inflation, against 56% who are not. That net score of -13 points compares with a net positive of 6 last October and 1 last July.

The coalition has slipped into negative territory. The proportion of people who think the coalition is doing a bad job is bigger than the proportion who think it is doing a good job: 46% to 41% – a net rating of -5.

In August last year it had a rating of +10.

Tories like the coalition, giving it a net positive of 71 points. Labour voters do not: a net negative of -56. Lib Dem opinion is mixed. Among current Lib Dems the coalition has a positive of 26 but among all people who backed the party in 2010 it is -9.

Coalition leaders are becoming more unpopular too. Cameron continues to be an asset to his party with a net positive rating among all voters of +5. But more people now think George Osborne is doing a bad job than a good one: a net rating of -2. Nick Clegg trails in with a net of -18.

Ed Miliband is also much more unpopular than Osborne, with a negative of -13. Among people who voted Labour in 2005 50% think he is doing a good job; among current Labour voters 58%.

ICM Research interviewed a random sample of 1,014 adults aged 18+ by telephone on 23-24 March 2011. Interviews were conducted across the country and the results have been weighted to the profile of all adults.