It was not a great start. Within minutes of signing a power-sharing deal with Morgan Tsvangirai, Robert Mugabe delivered another of his rants against Britain, blaming Zimbabwe's former colonial power for its desperate economic plight and making gratuitous digs at an opposition which "wants much more than it deserves".

He offered no hint of the humility, or the recognition of his own grievous mistakes and misrule, that will be necessary if Zimbabwe's cumbersome new power-sharing arrangements are to work. He barely acknowledged his supposed "co-leader". Indeed, the only talk of reconciliation came from Mr Tsvangirai.

For the moment the jury is very much out on this supposedly-historic deal, with the onus firmly on Mr Mugabe to prove that he is genuinely prepared to work with his old enemy - a man he has had imprisoned, tortured, beaten and charged with treason - for the benefit of all Zimbabweans.

If western nations are to give the billions required to rebuild Zimbabwe's shattered economy and if the three million Zimbabweans who have fled their country are to be enticed home, they will first need convincing that Mr Tsvangirai really is in charge and that Mr Mugabe is not simply using him as a front man to give a veneer of respectability to a vile regime.

To do that Mr Mugabe will have to accept the swift reversal of some of his regime's most heinous policies - the draconian security measures, the obstruction of humanitarian aid agencies, the repression of the media. He will have to call off his war veterans and end the intimidation of Mr Tsvangirai's supporters in the Movement for Democratic Change.

He will have to agree with Mr Tsvangirai an emergency plan to curb an inflation rate in excess of 20 million per cent and ways to restore to productive use the white-owned farms the regime has seized, plundered and ruined in the past eight years. He will have to engage in good faith in a process of constitutional reform leading to free and fair elections.

Were Mr Mugabe to do these things there would be real hope that Zimbabwe's long nightmare is over and Mr Tsvangirai's decision to share power with a man who has done so much to destroy his country will be justified.

But in 28 years Mr Mugabe has never previously shown the slightest inclination to compromise with his enemies and the ambiguities of this power-sharing deal - with Mr Mugabe heading the Cabinet as president and Mr Tsvangirai heading a Council of Ministers as prime minister - gives the wily octogenarian plenty of scope for obstruction and for outmanoeuvring his tactically far-less-astute rival.

Such a course might buy Mr Mugabe a little more time in office, but at a terrible cost to his desperate, starving people.

Times Recommends

• UN may halt 400-year-old 'freedom of the seas'
• Where the Rosetta belongs can’t be set in stone
• Gas deal on hold, but Ukraine may pay in the end