Morgan Tsvangirai is due to arrive in London today as Prime Minister of Zimbabwe. He will be seeking UK government support and pitching for foreign investment. How should we respond to such an appeal from a Government that is led by Robert Mugabe, a man to whom we have got used to saying “no”?

We are clear that we must support the new inclusive Government, whatever our strong doubts about Mr Mugabe. Mr Tsvangirai has bravely chosen to join a government with his erstwhile rivals as the only way forward for Zimbabwe.

The reformers who have faced torture and death in pursuit of democracy have chosen to make this Government work. We must find ways to support them, not least because the humanitarian crisis is still unfolding: a direct consequence of mismanagement and corruption.

Agriculture and public health do not recover overnight. Up to seven million people received food aid at the height of the recent hungry season, and more than 4,000 have died out of almost 100,000 cholera cases. To tackle this, the UK recently pledged a further £15 million in humanitarian assistance. All our support has been transferred through the UN and NGOs, not the Zimbabwean Government. President Obama offered generous US assistance on the same terms when Mr Tsvangirai visited Washington a few days ago.

But we must also engage politically. Mr Tsvangirai and Mr Mugabe have overcome many of the early setbacks and declared their common commitment to the global political agreement (GPA) that they negotiated under South African leadership with the help of their southern African neighbours. It is not perfect, but it does provide a programme of steps to be taken before fresh elections under a new constitution, which the agreement specifies should be completed within 18 months. If those steps are taken, it is a basis for the international community to step up engagement and support in response. By engaging with those committed to reform, we can press for this timetable to be met.

This is why we have met Mr Tsvangirai, his Finance Minister, Tendai Biti, and his Foreign Minister, Simbarashe Mumbengegwi. We discussed how the UK can help Zimbabwe to implement its own commitments under the GPA, particularly on constitutional reform, human rights and the rule of law. When in London, Mr Tsvangirai will meet business leaders as well as the Prime Minister.

But the inclusive Government must understand the context of UK support. Our assistance depends on it meeting its commitments. This in turn depends on Mr Mugabe honouring the agreements he has made with Mr Tsvangirai and the Zimbabwean people. There is still much to do on this. The media are still not free, political activists are still harassed, farm seizures continue and promised personnel changes in key positions have not happened. The EU has also made clear that its support depends on real progress on human rights and related issues.

We have heard calls for the immediate removal of sanctions against Zimbabwe. Let's be clear what those “sanctions” entail. They were never aimed at the Zimbabwean people. Restrictive measures were directed against individuals associated with the old regime's corruption and violence, and against companies that bankrolled that regime. While we can show some flexibility, such as allowing some Zanu (PF) ministers who are covered by the EU travel ban to accompany Mr Tsvangirai to the UK, we will not lift the bulk of these measures until we are convinced that Zimbabwe's transition to democracy has reached a point of no return.

Zimbabwe has begun the process of re-engagement with the IMF, World Bank and African Development Bank, and we are encouraging this. While misrepresented by some in Zimbabwe as sanctions, these assistance programmes always depended on the performance and credibility of the Government's economic programme, which is now back on track. It was Zimbabwe's unpaid debts to these institutions, not British opposition, that prevented them helping.

We welcome the efforts of President Zuma in South Africa, as well as other neighbours, such as President Khama in Botswana, to provide political and economic support to Zimbabwe's transition. The Southern African Development Community (SADC) must stand up for the GPA agreement that it sponsored and insist that both sides keep their commitments. We remain happy to follow their political lead; we recognise that the UK can easily set back change inside Zimbabwe by appearing too intrusive.

By entering a government with Mr Mugabe, the Movement for Democratic Change has taken a leap of faith. It is beginning to make it work, although there are plenty of pitfalls. Mr Mugabe could easily try to go back on his word and grab absolute power again. Nevertheless, it is time to show a little faith and get behind the agreement to build a new Zimbabwe, while keeping all sides to their commitments on economic and political reform. As President Reagan once said in another context, “trust but verify”.

Lord Malloch-Brown is Minister for Africa, Asia and the UN

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