Tony Blair must take a harder stance against South Africa's failure to condemn Zimbabwe, says a Labour MP.
Robert Mugabe defended the township demolitions
Kate Hoey was speaking after secretly visiting Zimbabwe to report for BBC Newsnight on how people are being forced to demolish illegal houses.
She said Mr Blair should stop South African President Thabo Mbeki from attending the G8 summit unless he condemns the Zimbabwe "excesses".
The Foreign Office says Mr Mbeki is an important partner on other issues.
It has not yet been confirmed that Mr Mbeki will attend July's summit of the G8 industrialised nations in Gleneagles, Scotland, although he has been invited.
'Wrong diplomatic approach'
A two-day general strike was called in Zimbabwe in protest at the township demolitions, which the United Nations says have left 200,000 people homeless.
But Zimbawean President Robert Mugabe has described the three-week blitz as "a vigorous clean-up campaign to restore sanity" in Zimbabwe's cities.
Ms Hoey told BBC News she had seen people being forced to knock down parts of their homes where displaced farm-workers were living.
And she said Mr Blair must press South Africa to use its influence on Zimbabwe.
"I'm afraid we've been hearing that he [Mr Mbeki] got a quiet diplomacy attitude for some years," she said.
"I think the time has come, particularly now with the prime minister being in charge of the G8 and the European Union over the next three or four months, that it's absolutely crucial that pressure is put on South Africa.
"They are the key to the changes that can happen in Zimbabwe.
"And the question of how that happens is, frankly, it's got to be worked out before we start talking about making poverty history."
Helping Africa is a key priority of the G8 summit and the Foreign Office stressed South Africa was the largest economy on the continent.
It is also a founder member of the New Plan for Africa's Development.
A Foreign Office spokeswoman said: "Mr Mbeki is an important partner on a range of international issues.
"As with all relationships, there will be some issues of disagreement and of marked disagreement and they have got to be managed."
She said Mr Mbeki had showed his determination to pursue good governance in Africa by sacking his deputy over corruption claims.
Foreign Secretary Jack Straw said he deplored the "horrific and ruthless actions of the Zimbabwean Government, who have ruined the lives of thousands of innocent families, condemning them to homelessness".
He said the acting Zimbabwean ambassador had been summoned to the Foreign Office this week to hear Britain's "outrage" and similar views had been expressed to the Zimbabwean vice-president.
Mr Straw added: "This week we and European partners froze the assets of more members of the Mugabe regime and banned them from travelling.
"Britain will continue to work with the International Community to restore democratic governance, human rights and the rule of law to the people of Zimbabwe."