Outside the Rainbow Towers Hotel in Harare, inflation has surged past two million per cent and children survive on a bowl of gruel a day. Inside, flowers have been ordered for a ceremony. President Mugabe and Morgan Tsvangirai, Zimbabwe's opposition leader, have met face to face for the first time since power-sharing talks began three weeks ago. President Mbeki of South Africa has flown in and out again, but with a promise to return.

A deal to end Mr Mugabe's stranglehold on power appeared tantalisingly close last night. Having implored Mr Mbeki to take his role of mediator more seriously, Zimbabwe's neighbours and the wider world will have little choice but to accept whatever may be agreed. But no pact will prove a viable basis for rebuilding the country unless the man who has brought about its demolition truly relinquishes control. Mr Tsvangirai can make this happen, but he must hold his nerve.

Three main sticking points have slowed progress towards an agreement: Mr Mugabe's reluctance to accept a purely titular presidency; bargaining between his Zanu (PF) party and Mr Tsvangirai's Movement for Democratic Change (MDC) over ministerial portfolios in a new government of national unity; and disagreement over whether to hold new elections in two years or five.

There is only one acceptable resolution to the first of these disputes. Mr Mugabe must give way. Having stolen an election from the MDC and disgraced himself and his security forces with a subsequent campaign of terror, he will be luckier than he deserves to remain in office even as a figurehead, as has been mooted. To cede only some of his executive powers to the new post of prime minister proposed for Mr Tsvangirai would not only mock the hopes of all who have voted against Mr Mugabe and suffered under him. It could also condemn Zimbabwe to an indefinite feud between two rival power centres, reminiscent of the bloody struggle between Zanu (PF) and Zapu (PF) in the 1980s.

Mr Tsvangirai must therefore insist on full day-to-day management of any Cabinet assembled under him. He has said that he is willing to work with Zanu (PF) moderates. It remains to be seen if they and the MDC can co-exist in government. But it is essential that hardliners such as Emmerson Mnangagwa, the Minister of Rural Housing, and Augustine Chihuri, Zimbabwe's police commissioner, be removed from power. It is equally vital that the Joint Operations Command set up by Mr Mugabe to co-ordinate the suppression of dissent be dismantled rapidly.

The MDC's negotiators must, finally, stand firm against Mr Mugabe's attempt to delay fresh elections for five years. He has already boasted of his democratic credentials only to trample on democracy in practice. The MDC has won the right to form a government and seek a fresh mandate, free from intimidation, in two years.

Major concessions by the MDC in any of these areas will effectively leave Mr Mugabe in power. That would block the release of £1 billion in US and British aid. It would also leave Mr Mbeki with nothing to show for his heavily criticised “quiet diplomacy” towards his northern neighbour. Mr Mbeki is seeking to burnish his legacy almost as urgently as Zimbabwe needs aid. Mr Tsvangirai's hand may be stronger than he thinks.