Britain and its international allies will urge South Africa to cut off electricity supplies to Zimbabwe if Robert Mugabe steals the election in two weeks’ time, The Times has learnt.

Plans are being drawn up to persuade Zimbabwe’s allies to mount an economic blockade and diplomats are considering a ban on the children of the elite going to school in Europe if Mr Mugabe loses the election but refuses to step down.

Concern is growing at the scale of the violence and intimidation before the rerun of the presidential election on June 27, with David Miliband, the Foreign Secretary, describing yesterday as “sadism” the murder and torture in the country.

Mr Mugabe vowed at the weekend that Zimbabwe would never be ruled by his “puppet” opponent, Morgan Tsvangirai, the leader of the opposition Movement for Democratic Change (MDC). Mr Tsvangirai has been detained five times over the past ten days. The MDC says that 66 of its supporters have been killed since the first-round polls in March.

Gordon Brown, commenting yesterday on the action against Mr Tsvangirai and the MDC, said that it was “further proof, if it is needed, that Robert Mugabe is becoming more blatant in his attempts to steal the 27 June election”.

Diplomatic sources recognise that the run-up has become so bloody that the election might not be able to proceed. They still profess hope, however, that Mr Mugabe will be unable on polling day to overturn his opponent’s adavantage of 47.9 per cent to 43.2 per cent.

Private opinion polls are being quietly held in Zimbabwe; diplomats hope that the results can be used to show a decisive lead for Mr Tsvangirai and employed in the propaganda war during polling weekend.

Diplomats are also optimistic that individual polling stations will display the results of their ballots, making it more difficult for numbers to be altered in Harare before they are announced.

Mr Miliband spoke over the weekend to Ban Ki Moon, the UN Secretary-General, as part of efforts to increase the number of African election observers from 150 to 400.

Mr Mugabe was quoted in the state-run Sunday Mail as saying that he would be willing to hand power to a ruling-party ally when he was sure the country was safe from “sellouts” and from British interference, although he put no timing on such a decision.

The Foreign and Commonwealth Office is also drawing up a range of options in case the President refuses to go. It is hoping to persuade Zimbabwe’s neighbours to create an economic blockade. Vital imports have to come through Mozambique and South Africa. “One way or another, this summer is likely to mark the endgame for Robert Mugabe,” one diplomat said.

British diplomats are talking up their chances of building a wide coalition in case of the need for action, in the knowledge that this cannot be presented to Zimbabwe solely as a British issue. African statesmen, including the former Presidents of Nigeria, Botswana, Mozambique, Malawi, Tanzania and Benin, along with Kofi Annan, the former UN Secretary-General, signed a declaration on Friday expressing concern at the violence and calling on African leaders “at all levels” to oversee the election.

Privately, countries such as Nigeria have told diplomats that they are concerned at Zimbabwe’s effect on Africa’s reputation; the US has also been tough. Even China, which signed a trade deal with Zimbabwe, made a “helpful” intervention at a UN debate last Thursday, diplomats said.

Some of Zimbabwe’s intermittent electricity comes from South Africa, and diplomats believe that they might be able to persuade the South African Government to restrict or turn off the supply. Although this has been seen as tantamount to declaring economic war, public opinion has changed because South Africa is experiencing its own power shortages. There is also opposition to the sale of electricity to Botswana and Mozambique as well as Zimbabwe.

British officials are also examining ways of widening sanctions against Zimbabwe in ways that will not hurt the population further. Plans to freeze the financial assets of the Zimbabwean elite, in ways similar to those used on North Korea and Iran, are being considered.

The European Union may follow Australia in banning the children of the country’s leaders from being educated in member states. A military intervention is highly unlikely unless there is a “complete breakdown of law and order”.

Officials recognise that South Africa will be critical in attempts to put pressure on Mr Mugabe to go. That President Mbeki is still close to the Zimbabwean leader is seen as a problem.

Jacob Zuma, the president of the ANC, has been significantly more sympathetic, appearing publicly with Mr Tsvangirai and offering support. Mr Zuma wields considerable influence inside South Africa because he is regarded as the heir apparent before elections next year, and is already operating a “shadow government”.

Ways the world can act

Existing sanctions:

— Travel ban on about 100 top Zanu (PF) officials and executives. Ban does not cover world diplomatic conferences, hence Mr Mugabe’s recent appearance at the UN food summit in Rome

— Seizing of some assets

Future sanctions may include:

— Widening of travel ban to include relatives of Zanu (PF) members thought to be involved in human rights abuses

— Children of officials prevented from attending schools overseas

— Freeze bank accounts and assets held in US or EU by regime members, officials and relatives

— Complete trade embargo and ban on purchase of goods

— Action against Western companies maintaining a presence

— Freezing all aid

— Increased pressure on neighbouring states to suspend Zimbabwe from the Southern African Development Community

— Pressure on China to break off Zimbabwe relationship, which has allowed it to mitigate the impact of the current sanctions

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