The Prime Minister told the Commons that the "only credible" election was the earlier one, in which the opposition "MDC recorded a victory".

He welcomed the African Union's call for an end to violence and mediation, before setting up a "transitional" government.

"Having talked to the UN Secretary General, I think it's right that the UN send an envoy to Zimbabwe. In the absence of real change we will step up our sanctions and ask other countries to do so," he warned.

"We will press for tough action on Zimbabwe at the Security Council later. We will do so at the G8 in the coming days."

Mr Brown was replying to Labour's Chris Bryant who branded Mugabe a "corrupt and brutal thug".

Mr Bryant said Mugabe proved "that you can put your hand on the Bible and swear an oath and smile and smile and still be a complete and utter villain.

"But the UN has been far too slow and reluctant to adopt a robust attitude to Mugabe."

Mr Brown said: "The only credible election that has taken place was the election in which the MDC actually recorded a victory.

"Given that the second round was a travesty at the hands of what is a blood-stained regime, I'm pleased that the African Union called for an end to violence, set up a system of mediation and were talking about a transitional government in Zimbabwe."