The Times reported that two plans have been drafted by Britain's Ministry of Defence (MoD) following a request from the department's crisis management team.
According to the British newspaper, Britain has a plan to deploy troops in Zimbabwe to resolve a humanitarian crisis and a separate plan to evacuate British nationals and their dependents.
The ministry said on Tuesday it had no current plans for military action in Zimbabwe but declined to discuss whether contingency plans had been drawn up.
Michael Ellam, Prime Minister Gordon Brown's spokesperson, insisted that the UK was not preparing a military response. "I don't think we should get too far ahead of ourselves," Ellam said. "This is not a plausible course and not one that would enjoy international support."
Paddy Ashdown, a former UN High Representative to Bosnia and a British peer, said military action could be needed to avoid an humanitarian crisis but suggested that Britain should not be involved because of its history as Zimbabwe's colonial ruler.
However, Ashdown said a diplomatic solution was still possible, particularly if South African President Thabo Mbeki - the chief negotiator - was prepared to take a harder line with Mugabe.
"The key person in this is Thabo Mbeki and so far his silence has been thunderous," Ashdown told the British Broadcasting Corporation (BBC) radio.
Britain's Africa minister Mark Malloch-Brown said on Monday that military action would be implausible, ineffective and unlikely to win international support.
The Times quoted a former British Royal Marine commander as saying military action could be justified but would likely be complicated by the need to secure flying rights over neighbour countries.
It is not clear how many people Britain would need to evacuate under any intervention plan. Britain's Foreign Office said there were about 2 000 registered British nationals in Zimbabwe but that it has pledged support to a total of 14 000 UK passport holders and others eligible to apply for British citizenship. Around 5 000 of those were people over 60, the department said.