Chancellor Gordon Brown has rejected accusations that the government's �43bn spending bonanza is based on over-optimistic economic forecasts.

Speaking the day after unveiling his Comprehensive Spending Review, Mr Brown dismissed Conservative charges that his spending plans would force up taxes and relied on predictions of a buoyant economy.

These promises could not be delivered if the economy didn't perform as well as Gordon Brown is predicting Shadow chancellor Michael Portillo

Mr Brown told the BBC the plans stood because he had "been cautious" in his projections.

Later in the day, in Prime Minister's questions, Mr Blair went on the offensive over the �43bn spending boost, saying the government was committed to improving public services while the Tories' spending cuts proposals were "political hara-kiri."

The hoped-for shine was taken off media coverage of Mr Brown's four-year boost to public spending by a new leak of a private memo to the prime minister from one of his closest advisers, Philip Gould.

Policing plans unveiled

Mr Brown's defence of his plans came on the same day Home Secretary Jack Straw revealed how his department will use its �2.5bn share of the new cash to boost police recruitment.

The chancellor insisted his programme of investment into frontline public services over the coming years would stand.

"It is based on a long term plan of equality on opportunity for all, not just a few," he said.

Denying that Labour had returned to "tax and spend", he explained how the extra money would filter into the system.

"The big change I announced yesterday is whereas every additional pound spent by the last Conservative government, 42p went on unemployment, social security and debt interest payments.

"Because we have cut unemployment and debt, only 17p of every additional pound is having to be spent on these things.

"That leaves 80% to go on health, education social services, transport and all the public services that people want to see improved."

When questioned on the veracity of his economic forecasts Mr Brown said: "Our proposals will be met, we have been cautious.

"We are assuming a more cautious estimate of growth than we are actually getting at the moment."

Tax and spend

But shadow chancellor Michael Portillo said Mr Brown's plans would put the economy at risk.

Labour had, he said, reverted to an old-style "tax and spend" party guilty of "splurging" on public services.

He told the BBC: "We are in the land of promises. What people know is the tax rises that they have already paid, and what we have for tomorrow is a lot of promises.

"These promises could not be delivered if the economy didn't perform as well as Gordon Brown is predicting."

Asked what alternative a Conservative government offered, Mr Portillo said: "My objective is that we should always allow public spending to grow, to grow in real terms, to put improvements into public services, but over a period of time to make sure that that rate of growth is within the rate of the economy."

'Tory cuts'

Mr Blair attacked Tory plans to impose spending cuts during question time, asking for details of where the �16bn worth of cuts would come from.

He said the Tories could not complain about rising police numbers, or demand smaller class sizes, if they did not support the necessary investment to deliver both.

"The dividing line at the election is now clear between a party willing to invest in our public services and �16 billion of cuts under you," he said.