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 racism against his government.
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 Zimbabwe's opposition Movement for Democratic Change, such as targeted sanctions.
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.
Facing Tory 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.
'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.
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.