LONDON, June 28 (Reuters) - Britain's Prime Minister Gordon Brown said on Saturday Zimbabwe's presidential election was a "new low" -- but predicted democracy will come to the southern African country.

A storm of condemnation from inside and outside Africa has greeted 84-year-old President Robert Mugabe's decision to hold Friday's election, in which he was the sole candidate.

"As Nelson Mandela has said, there has been a failure of leadership in Zimbabwe," said Brown in a statement, referring to the former South African President's comments on the Mugabe government in London earlier this week.

"Yesterday's attempt to hold an election was a new low," added Brown. "The world is uniting in rejecting the illegitimate regime of Robert Mugabe."

Britain is preparing proposals for tougher European Union sanctions on Zimbabwe that it will take to the next EU foreign ministers' meeting in July, but Brown also urged the African Union to take action at a summit in Egypt on Monday.

"We will work with international partners to find a way to close this sickening chapter that has cost so many lives," said Brown.

"The forthcoming African Union summit is an opportunity for the region to restore hope to the people of Zimbabwe. Democracy will ultimately prevail."

Zimbabwe opposition leader Morgan Tsvangirai and Western powers have denounced Friday's poll as illegitimate.

The U.N. Security Council has said it deeply regretted the staging of the election because free and fair conditions did not exist, and Nobel Peace laureate Archbishop Desmond Tutu said the world had the right to intervene to end the crisis. (Reporting by John Joseph; Editing by Charles Dick)

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