George Osborne last night identified the first public spending cuts he would make within weeks if the Tories win the general election, under plans to reduce the UK's record fiscal deficit faster than Labour.

Warning of the importance of starting the "heavy lifting" early on, the shadow chancellor pledged in a lecture to cut child trust funds and tax credits for wealthier families in the spring.

Osborne would be due to hold an emergency budget within 50 days of the election. But the shadow chancellor believes Britain's £178bn deficit imposes such a burden on the public finances that he would not wait for the budget to implement the first round of cuts, which he would expect to make within weeks of a Tory victory.

He said the biggest spending cuts, such as a pay freeze for five million public sector workers earning more than £18,000, would not be made until 2011, but he identified programmes that would be cut from this year if the Tories were to win.

"Programmes that represent poor value for money, excessive spending on things like advertising and consultants, spending on tax credits for people earning over £50,000, and spending on child trust funds for better-off families will all have to be cut during the financial year," Osborne said at the London School of Economics.

Labour plans to raise spending by £31bn in the 2010-11 financial year, which begins in April, a month before the expected election. Osborne believes this 2% increase in real terms is not credible with such a large fiscal deficit and such a slow recovery.

"Everyone knows the government's spending plans for next year are driven by a looming election and not economic reality," he said. "So, with the date of the general election increasingly likely to be after the beginning of the next financial year, that means we will need to make early in-year reductions in existing plans."

The chief secretary to the Treasury Liam Byrne said: "What is clear is that in his rush to cut spending in 2010, George Osborne would put the recovery in grave danger. But until he says how he'll do it, and whether he'll match Labour's pledge to halve the deficit in four years, his speeches must be taken with a huge pinch of salt."

"Tonight was another missed opportunity to come clean on how he'll pay for the £34bn of unfunded [Tory] tax and spending policies which he let the shadow cabinet run up while he was too busy running the Tory election campaign to keep them under control."

Byrne said Osborne appeared to hint he would shift from Labour's plan to halve the deficit by using two-thirds spending cuts and one-third taxes. Instead Osborne would adopt an 80:20 ratio, in favour of more cuts.

The Liberal Democrat Treasury spokesman Vince Cable said: "It's foolish to set a political timetable with no regard for the state of the economy. There's a big risk that if cuts begin suddenly and on a purely political basis the economy will be plunged back into recession.

"What is needed is a set of clear economic tests, which include the growth of the economy and employment, as well as conditions in international markets, to judge when contraction of spending should begin or be accelerated."