The agreement to create a power-sharing government that Robert Mugabe and Morgan Tsvangirai signed described the farm seizures as irreversible and said the British Government should "accept the responsibility to pay compensation for land acquired from former landowners for resettlement".
The British Foreign Office said it would support a fair process of land reform as part of a wider recovery package but insisted: "We have never agreed to accept responsibility for compensation."
Mr Mugabe began the often violent land seizures in 2000 to boost his fading popularity, accusing Britain of reneging on a commitment in the 1979 Lancaster House Agreement to compensate white farmers for land redistributed to blacks.
The move triggered Zimbabwe’s economic collapse as farms were plundered and ruined, and hundreds of thousands of black workers lost their jobs.
The compensation call has heightened fears Mr Mugabe is setting the tone for what is meant to be a government of equals.
Western sources said the power-sharing agreement was deeply ambiguous, with no clarity on the relative powers of the cabinet, which Mr Mugabe will chair as President, and the Council of Ministers, which Mr Tsvangirai will chair as Prime Minister.
Mr Mugabe will retain considerable authority.
He will chair a National Security Council, comprising the heads of the army, police and secret services, while Mr Tsvangirai will only be a member.
He will also retain the power to proclaim martial law and can allocate ministerial portfolios, make appointments and dissolve parliament "in consultation" with the Prime Minister.