Morgan Tsvangirai is to be sworn in as Zimbabwe's prime minister , pledging to take control of government, rescue millions from the brink of starvation and shunt President Robert Mugabe from power. Many Zimbabweans and some foreign governments, including Britain, fear the power-sharing administration is a trap that will only perpetuate Mugabe's rule.

The leader of the opposition Movement for Democratic Change today said that after months of wrangling with Mugabe over key cabinet posts his party compromised and agreed to join the government to prevent Zimbabwe collapsing under hyperinflation and the almost total ruin of agriculture and industry that has left seven million people, two-thirds of the population, reliant on foreign food aid.

Tsvangirai said joining a coalition with the man who used violence and intimidation to deny the MDC power was not an end in itself but a step toward democratic government.

"We are not joining Mugabe. This is part of a transitional arrangement, negotiated. Mr Mugabe has executive authority. I have executive authority," he said. "The MDC cannot be authors of chaos by allowing the country to go over the precipice. That's where it is... We are aware of the shortcomings [of sharing power] but we are also aware of the potential of responding to the needs of the population of Zimbabwe."

The power struggle that has marked political negotiations is, however, likely to continue in the new administration.

Under the coalition agreement, Mugabe remains president, with Tsvangirai overseeing the daily administration of government as prime minister. Cabinet seats are almost equally divided with a small breakaway MDC faction also represented.

Mugabe won the struggle to retain control of the principal security ministries, particularly defence and justice, which sceptics fear he will continue to use as tools to attack and intimidate his opponents.

Authority over home affairs, which is seen as crucial to ensuring future elections are free after the widespread violence by Mugabe's supporters in last year's ballot, is to be shared.

The MDC has control of the finance ministry and most social affairs ministries, such as health, which could prove an asset if the new government is able to deliver improved services.

Tsvangirai's main concern will be to put a new constitution in place and for fresh elections within two years in which he is counting on an embittered electorate to deliver such a decisive rejection of Mugabe that he will be forced to accept defeat.

For now, the new prime minister faces a myriad of challenges, including 94% unemployment, the worst harvest since independence and a currency so worthless that shops will only accept US dollars and South African rand.

Tsvangirai said the most important cabinet post for reviving Zimbabwe's fortunes was that of the finance minister and named the MDC's secretary general, Tendai Biti, for the job.

Biti, a lawyer and the MDC's chief negotiator, is expected to use the power the finance ministry wields with its control over budgets to influence Mugabe's ministers.

His appointment is also likely to go some way to reassure foreign donors, principally Britain and the US, whose money is seen as key to Zimbabwe's revival but who are sceptical over Mugabe remaining president.

Britain has taken the highly unusual step of publishing a notice in the Zimbabwean press laying out its concerns about the new administration. While saying that "it is not for the United Kingdom to accept or reject anything", the notice goes on to say that it regards any administration involving Mugabe as unacceptable.

"Given Mugabe's resistance to change to date, his failed economic policies and his propensity to rail against the outside world, it is unlikely that any government involving Mugabe will inspire donor confidence and attract the support it so badly needs," the notice placed by the British embassy in Harare said.

Britain says it wants to see the new administration "reverse the political, economic and social decline" as a condition for aid. The MDC says it can't do that without considerable financial support.