British Prime Minister Theresa May said the resignation of president Robert Mugabe on Tuesday gave Zimbabwe "an opportunity to forge a new path free of the oppression that characterised his rule".
"In recent days we have seen the desire of the Zimbabwean people for free and fair elections and the opportunity to rebuild the country’s economy under a legitimate government," she said in a statement.
"As Zimbabwe's oldest friend we will do all we can to support this, working with our international and regional partners to help the country achieve the brighter future it so deserves."
Mugabe, who had led Zimbabwe since independence from Britain in 1980, resigned as president on Tuesday as parliament began impeachment proceedings in the wake of a military takeover.
Welcoming his decision, British Foreign Secretary Boris Johnson added to May's call for free and fair elections.
"I will not pretend to regret Mugabe’s downfall: but this can now be a turning point, a moment of hope for this beautiful country, full of potential," he said.
"The immediate priority is to ensure that Zimbabwe has a legitimate government, appointed through free and fair elections in accordance with the constitution."
Johnson pledged that Britain stood "ready to support Zimbabwe in this goal."
Last week, he also expressed hope for change in the country, but warned that "nobody wants simply to see the transition from one unelected tyrant to the next".