Gordon Brown attempts to launch a political fightback today by declaring that he takes "full responsibility" for his role in the banking failures that led to the global recession, and claims that the downturn marks the end of the era of laissez-faire government.

In an interview with the Guardian, the prime minister concedes that in retrospect he wishes he had mounted a popular campaign 10 years ago to demand more responsible regulation of the world's financial markets. He attempts to draw a line under calls for him to make an apology by admitting that the national system of regulation he helped establish in 1997 could not keep pace with the massive global financial flows.

In some of his most extensive comments on his role in the recession, Brown said: "I take full responsibility for all my actions, but I think we're dealing with a bigger problem that is global in nature, as well as national. Perhaps 10 years ago after the Asian crisis when other countries thought these problems would go away, we should have been tougher ... keeping and forcing these issues on to the agenda like we did on debt relief and other issues of international policy."

Brown spoke at the start of a major Guardian series on Labour's future. David Cameron, the Conservative leader, has exploited the prime minister's reluctance to make an apology, a tactic which has helped give him a double-digit lead in the polls.

Brown's remarks will, he hopes, give the party a launchpad to retaliate, insisting that it "is essential for the sake of the country" that Labour wins a fourth term at the next general election, likely to be held next year.

He argues that "only progressive, centre-left governments can address the problems of the global change".

Brown also claims that "the 40-year-old prevalent orthodoxy known as the Washington consensus in favour of free markets has come to an end", but signals a refusal to return to Labour's comfort zone by saying there will be no return to "big government", or any let up in public service reform.

"Laissez-faire has had its day. People on the centre-left and the progressive agenda should be confident enough to say that the old idea that the markets were efficient and could work things out by themselves are gone", he says.

The Guardian has learned that ministers have separately conceded that the government is now unlikely to go ahead with a planned spending review this summer, partly because the economic outlook is so unstable that it is hard to make meaningful three-year spending forecasts department by department in Whitehall.

During the interview, Brown:

• Refuses to rule out a further British economic stimulus in the April budget. He promises extra help for hard-pressed savers and says ministers are looking at offloading further public assets in the budget in a bid to balance the books.

• Defends reforms to the part privatisation of the Royal Mail, saying it is right to find an international investor to help with new international investment.

• Insists the G20 summit in London on 2 April will determine whether the world collapses into protectionism. This, he says, would be "the road to ruin", parallel to the failed London economic conference in 1933 that made recession a fact of life for the rest of the decade.

• Says the summit will agree new ground rules to control not just the structure of executive pay, but their absolute levels. He also claims the summit will also signal "the beginning of the end of the offshore tax havens and banking secrecy".

• Seeks to dispel notions of a split between the US and mainland Europe on whether to back a specific co-ordinated further economic stimulus linked to each nation's GDP, saying: "It is not about numbers, but about commitments by each continent to coordinate their action."

The prime minister also argued that the world recession was changing the public's expectations of business values, and they no longer believe a successful economy has to be based on high levels of risk.

"Most people want business to have the same values as they practise in their everyday life. People would rather reward hard work rather than risk-taking. They want to support enterprise and not excess. They want to support people that take responsibility and not run away from it".

Giving his fullest defence of his role in the recession, and his refusal to offer an outright apology, he said: "I take full responsibility for all my actions."

The prime minister said: "We created a system in 1997 which was unified regulation. Before 1997 it was virtually self-regulation. We created a statutory system, but around the world we were finding that we had a global set of financial flows and you needed global supervision."

He added there had been a wider general intellectual failure to understand the dangers of these sophisticated markets.

"The general view of financial practitioners was that the more ownership of products was diversified, the more you limited the danger of risk falling on one institution.

"But actually because of the entangled nature of the financial institutions, what was designed to spread risk actually spread contagion."

He defended his role in bailing out the banks, saying he had saved them from collapse and claimed his government was the first in the world to impose quantitative targets for lending amounting to £50bn this year to banks in which the government holds shares.