The two sides signed a power-sharing deal last month, but the new government has yet to be formed as they haggle over which party gets which ministries.

An official close to the presidency said the dilution of Mr Mugabe’s powers promised in the agreement was "illusory", and described the MDC as merely a "junior partner" whose only role would be "to gain legitimacy and international funds".

His comments appear to justify the fears of Western diplomats who were expressing doubts about the agreement within days of it being signed – and point out that Morgan Tsvangirai, the MDC leader, won the first round of the presidential poll in March.

A ministerial post involving kick starting foreign aid is seen by some as a poison chalice for the MDC. If the party were to succeed it would help shore up support for the planned Mugabe-led coalition government, making it harder to oust in future. If it failed, it would be branded incompetent – also undermining its own support.

In negotiations which have dragged on for weeks, Mr Mugabe’s Zanu-PF party is sticking to a shopping list of ministries for itself which would include the departments of defence, justice, home affairs, farming and information. It also wants the mines ministry, the last occasionally functioning sector of the economy given the country’s wealth of natural resources, which carries huge opportunities for corruption.

The MDC, meanwhile, would be offered the finance ministry, in an effort to persuade donors that real reform was taking place and trigger billions in aid and reconstruction that have been promised.

"It’s a tricky situation for the MDC," said the presidential official. "Nonetheless we now have the opposition in government and they have to fix the economy, just as they told the electorate.

"When you look at the events on the ground they have little leverage to drive the political agenda and it’s not going to be easy for Britain to own up to its promises because, they are frustrated judging from remarks coming out of Downing Street.

"If it wasn’t for the dire economic situation Mugabe would never share power. Frankly speaking, the world might celebrate that his executive powers have been diluted but that is illusionary. The opposition are junior partners and more of ceremonial, but at this point we need them to gain legitimacy and international funds."

A senior member of Zanu-PF’s politburo, the party’s supreme decision-making body, added: "Tsvangirai boasted prior to the March presidential polls that his Western friends, in this case the British, will give him money and as such could repair the economy in 100 days.

"Zanu-PF will make him walk the talk to deliver economic aid from Britain no matter how slowly it trickle in. Also the MDC will be forced to negotiate the lifting of EU sanctions against government officials which the British led the EU into enacting."

MDC officials are aware of the risk of being manipulated and say they will not sign up to a ministerial division that does not give them real authority.

"It would appear that Zanu-PF does not understand power-sharing," said MDC spokesman Nelson Chamisa. "We are still poles apart, with them insisting on taking all the key ministries, literally rendering the (opposition) peripheral in government – in fact, a situation where we would be in but out of government."

Western diplomats have long offered the carrot of aid in exchange for deep reforms in the policies that have destroyed the country’s economy, and since the deal was agreed have warned that the new government, if and when it is formed, will have to show that it is making a break from the past before aid starts flowing.

"We want to support this, we want to see it work," said one. "Zimbabwe doesn’t have any more time." But he warned: "We need some evidence that there has been a political change. We will not fund Zanu, we will not pay them to stay in office, but we will pay for their mistakes. We need to see Tsvangirai deliver change."

Officially Zimbabwean inflation is running at 11.2 million per cent a year, but according to according to US economist Steve Hanke, a professor of applied economics and fellow of the Cato Institute in Washington, who uses a special index derived from market-based data, the figure reached a stratospheric 531 billion per cent last month. The Sunday Telegrapg