Details began to emerge today of the deal that could end Robert Mugabe’s 28-year monopoly on power, after the veteran Zimbabwean president agreed to a government of national unity with his political foe, Morgan Tsvangirai.

The potentially historic deal, announced last night by President Mbeki of South Africa, will, if carried out, end the political crisis triggered by hotly-disputed presidential elections earlier this year.

David Coltart, a senator for Mr Tsvangirai’s Movement for Democratic Change, said that a constitutional amendment would soon be moved in the Zimbabwean parliament to establish an inclusive government. That government would start an 18-month process of reform to implement a new democratic constitution and a time frame for fresh elections.

Western powers have questioned whether Mr Mugabe truly intends to relinquish his iron grip on Zimbabwe. The 84-year-old has insisted that he must remain as president while Mr Tsvangirai becomes prime minister, and while the MDC says he must relinquish most of his powers it is unclear whether he has agreed to do so. A master of political intrigue, Mr Mugabe has outwitted his opponent many times in the past.

Mr Coltart said that Mr Mugabe would have “greatly reduced powers to those he enjoys today”. There would also be two largely ceremonial vice-presidents from Mr Mugabe’s Zanu (PF).

As prime minister, Mr Tsvangirai “does not have absolute power but he does have substantial power”, Mr Coltart, who was present at the launch of the MDC nine years ago, said.

Mr Tsvangirai is to advise Mr Mugabe on all future appointments such as judges and ambassadors, though whether he will be able to compel the president to heed his advice is uncertain.

Underneath Mr Tsvangirai will be two deputy prime ministers, one from MDC-T, Mr Tsvangirai’s faction, and one from MDC-M, a rival faction headed by Arthur Mutambara.

Mr Coltart admitted the arrangement for conducting government business – at the heart of the impasse of the last weeks’ negotiations - was “slightly cumbersome”. Mr Mugabe is to chair the Cabinet, while Mr Tsvangirai will be the vice-chair. The Cabinet will largely reflect the votes cast for the various parties in the March election – in which Zanu PF claims it got the most votes, if not the most parliamentary seats.

Zanu PF will have 15 seats while MDC-T will have 13 and MDC-M three.

“If the two MDC factions work together, which they must in the national interest, they will enjoy a majority in Cabinet,” said Mr Coltart, who is a senator for Mr Mutambara’s faction.

The work of the Cabinet will be overseen by a council of ministers headed by Mr Tsvangirai. A source close to the talks quoted by Agence France-Presse said that all decisions would be made by the council, though it would have to report back to Mr Mugabe.

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