The weekend meeting of Commonwealth leaders achieved the "outcome we wanted" on Zimbabwe, the prime minister has said.

Tony Blair said it was "inconceivable" that the country could have returned to the Commonwealth council given the actions of the Zanu PF regime.

The prime minister told the House of Commons that "Zimbabwe has gone backwards" since its suspension and had no right to remain a full member of the Commonwealth.

The presidency of Robert Mugabe was driving the "country further and further into chaos", MPs were told.

Stressing the need for regime change, Blair said Mugabe's decision to leave the Commonwealth showed how isolated the country had become under his corrupt leadership.

But he stressed that the "strong bonds between the Zimbabwean people and the Commonwealth" would remain despite the serious diplomatic rift between London and Harare.

"There will always be a place for a democratic Zimbabwe in the Commonwealth," said Blair.

"Britain remains the leading cash donor for the UN humanitarian programmes inside Zimbabwe."

For the opposition, Michael Howard said ministers had been "behind the game" in taking action against Zimbabwe.

"The government' hasn't led, it's followed and the people of Zimbabwe are the worse for it," he said.

He went on to warn that European Union sanctions "are still not tough enough".

Howard called for the sanctions to be extended to cover the "businessmen who still bankroll Zimbabwe".

"The leverage of the Commonwealth is diminished given Mugabe's decision to withdraw," he said.

"Is there not now a powerful case for the United Nations to become more actively involved."

Liberal Democrat leader Charles Kennedy said the government should have "taken a harder line at an earlier stage".

He described Zimbabwe's current isolation as the "sad but inevitable" consequence of Mugabe's regime.

Despite the row over the future membership of Zimbabwe, Blair said significant progress had been made in tackling the problems facing the 53 members.

He said the Commonwealth nations had united behind a call for a fresh push towards world trade talks.

Heads of government had shown a "collective commitment Doha" trade round, MPs were told.

The consensus achieved in Nigeria revealed "that a global deal is indeed possible".

But Blair went on to stress that "the world's poor will be the biggest losers" if the obstacles to an agreement were not overcome.

The prime minister said the summit had recommitted the Commonwealth to the development goals - including a pledge to reduce the number of people living in poverty by 50 per cent by 2015.

But he went on to warn that heads of government had expressed growing concern at the spread of HIV/Aids.

"Three million people will die of the HIV/Aids virus this year alone," said the prime minister.

"It poses one of the greatest threats not just to health but to global development."

Blair said the British government was the world's second biggest donor to projects tackling the epidemic.

Britain had given £270 million in aid to tackle the issue in the in the last financial year, he added.