Britain and South Africa have reached agreement on Zimbabwe's suspension from the Commonwealth, Downing Street has said.

The deal followed talks between Tony Blair and President Thabo Mbeki at the heads of government summit in Nigeria.

Earlier, a deal on retaining the suspension of Robert Mugabe's regime appeared to collapse.

But following a meeting between the two leaders hopes that the agreement would be passed appeared to rise.

The Nigerian hosts and the other parties at the talks had been keen to avoid the impression of splits on the issue, and the potential for further embarrassment appeared to be receding on Sunday.

Earlier, the prime minister had made his position clear, saying: "I don't think anyone could see any possible justification for lifting the suspension now."

The British government has insisted that the human rights situation in Zimbabwe has deteriorated since its suspension last year.

Mugabe had vowed to leave the Commonwealth if his regime was not readmitted, but Blair said: "Whatever threats Zimbabwe makes I think people should treat them as they deserve to be treated."

And speaking to Sky News' Sunday with Adam Boulton programme, the prime minister said that the issue should not prompt Britain to consider leaving the Commonwealth.

"However difficult these meetings turn out to be I think it would be a very big mistake for us to leave the Commonwealth or treat it as of no interest or importance," he said.