Zimbabwe has "gone backwards" since it was first suspended last year from the Commonwealth, Tony Blair has told MPs.
The talks were heavy going, says Blair
Robert Mugabe announced Zimbabwe was quitting the Commonwealth after fellow members at their weekend summit agreed to suspend it indefinitely.
Mr Blair said the suspension decision taken in Nigeria was "hard fought but a victory for Commonwealth values".
Updating MPs on the Commonwealth talks, he said it was "inconceivable" for a "chaotic" Zimbabwe to be readmitted.
Zimbabwe was originally suspended from the Commonwealth over human rights abuses during elections
that returned President Mugabe to power.
South Africa, Mozambique, Namibia and Zambia opposed the decision to continue the suspension.
But Mr Blair stressed that every country had in the end signed up to the decision, giving the lie to President Robert Mugabe's claims of a British-led "white conspiracy" against black Africa.
Mugabe says his government is victim of racism
And he offered hope to a reformed Zimbabwe rejoining the Commonwealth.
"There will always be a place for a
democratic Zimbabwe in the Commonwealth," he said.
The prime minister highlighted the violence and intimidation facing those speaking out against Mr Mugabe since last year's initial suspension.
"The economic policies are driving the country further and further into chaos," he said.
Britain was trying to go along with the demands of Zimbabwean opposition party the Movement for Democratic Change, such as targeted sanctions.
Maximum pressure had to be put on Mr Mugabe, he said, but there were limits on what could be done from outside.
"The situation in Zimbabwe is such that in the end it is from within that the main change must come," said Mr Blair.
South Africa dispute
Facing demands for a greater United Nations role in trying to resolve the problems, Mr Blair pointed to the difficulty of securing agreement for a UN resolution.
And he took a diplomatic line when Tory MP Henry Bellingham asked why South African President Thabo Mbeki was being "so weak and so half-hearted" against Zimbabwe.
"There is a disagreement," he said.
"I think rather than engaging in an attack on the South African president, we had best simply to indicate why we feel so strongly that the right way to deal with this is to change the regime in Zimbabwe and work with other countries in doing that."
'Behind the game'
Conservative leader Michael Howard congratulated the prime minister on his "strong stand" at the summit.
But he criticised the government for not always taking the same stance, accusing it of being "behind the game" on the issue initially.
"It has not led. It has followed and the people of Zimbabwe are the worse for
it," he said.
Mr Howard complained that EU sanctions, like travel restrictions, against Zimbabwe were
still not strong enough.
He asked: "Why don't they include the businessmen who still
Liberal Democrat leader Charles Kennedy also said ministers should have taken a harder line towards Zimbabwe earlier.
And he urged Mr Blair to ensure Britain kept pushing to keep the options open for UN action.
Mr Mugabe's "chaotic and despotic" regime made the suspension decision inevitable, said Mr Kennedy.
Mr Blair also used his Commons statement to hail the agreement at the summit on the urgent need to relaunch the world trade talks, which stalled in September.
That commitment from both rich and developing nations "shows that a global deal is indeed possible", he said.
The need to tackle the "grave threat" of HIV/Aids, which was killing three million people a year, was another crisis highlighted at the summit, he said.
Pakistan is also currently suspended from the Commonwealth, another item on the summit's agenda.
Mr Blair said Commonwealth leaders had welcomed Pakistan's progress towards democratic government.
And they had voiced hope that its parliament would soon approve measures which would enable its return to the Commonwealth.