Foreign Secretary William Hague today commended the people of Zimbabwe for holding peaceful presidential polls, but voiced "grave concerns" about the conduct of the election, which delivered Robert Mugabe a further term in power.
Mr Mugabe won the election with 61% of the vote, with challenger Morgan Tsvangirai trailing on 34%, said the Zimbabwean Electoral Commission.
But Mr Tsvangirai alleged fraud and announced that his Movement for Democratic Change party would not participate in any government institutions in protest.
In a statement released by the Foreign Office in London, Mr Hague said: "People around the world are watching events in Zimbabwe, following the announcement by the Zimbabwean Electoral Commission that President Mugabe has won the presidential elections, as well as the indications of possible legal challenges.
"I commend the people of Zimbabwe on holding peaceful elections. However we have grave concerns over the conduct of the election.
"The preliminary statements of the African Union (AU) and Southern African Development Community (SADC) observation missions, and those of the domestic observer groups, have outlined many of these significant concerns, and I hope that their final assessments of the elections will take into account the full impact of these irregularities on the outcome."
Zimbabwe's Electoral Commission said that Mr Mugabe's Zanu-PF party won 158 of the 210 parliamentary seats, giving it a two-thirds majority in the legislature, which will enable it to make amendments to the new constitution.
Mr Tsvangirai has said he will challenge the result in the courts and called for the elections to be re-run.
And Mr Hague said that there were "serious" questions about the credibility of the election, because of irregularities both in the run-up to the ballot and on polling day itself.
Mr Hague said he was "deeply concerned" that a number of reforms promised in the 2008 Global Political Agreement setting out the terms of power-sharing between Zanu-PF and the MDC had still not been completed by the time of the presidential poll, despite being highlighted by SADC as "necessary for peaceful, credible, free and fair elections".
And he added: "We are also concerned with irregularities reported on the day.
"The AU preliminary report underlined in particular the strategic importance of the voters roll, and that by law it should have been made available to all political parties, yet observers saw no evidence that this was the case. This was a critical flaw.
"We also have concerns over reports of large numbers of voters who were turned away, particularly in urban areas, the very high numbers of extra ballot papers that were printed and additional polling stations apparently added on Election Day itself.
"The irregularities in the lead up to the elections and on election day itself, reported by the observer missions and in contravention of SADC's guidelines, call into serious question the credibility of the election. We note that some political parties have rejected the result on the basis of these irregularities.
"We will need to examine what has happened and consider further reports from regional and local observer missions. In the meantime, it is important that all allegations of electoral violations are thoroughly investigated. We will continue to support Zimbabwe and its people in their aspirations for a democratic, peaceful and prosperous future."