Two separate contingency plans for military action in Zimbabwe are held by the Ministry of Defence,The Times has learnt, although the Government insisted yesterday that intervention was not “a plausible course”.

One plan involves the deployment of troops into Zimbabwe to resolve a humanitarian crisis. The other is to provide military support if a national evacuation order to help British residents to leave the country was implemented.

The plans were drawn up as part of a general request for military options ordered by the Defence Crisis Management Organisation of the MoD. The military plans assume that a neighbouring African country would agree to play host to British troops and transport aircraft. Defence sources acknowledged that such an agreement in the current climate was unlikely.

Lord Ashdown of Norton-sub-Hamdon, the former international envoy, who gave warning yesterday of the risk of genocide in Zimbabwe, toldThe Times that if military intervention was agreed by the international community Britain could not take the lead role because of its colonial past. Lord Ashdown said that if genocide was threatened military intervention would have to be considered. “But it could not be undertaken without widespread support from Zimbabwe’s neighbours, in particular South Africa,” he said.

The main burden would have to fall on the neighbouring countries, with neither Britain nor the United States playing a leading role, he added.

Lord Ashdown and Lord Carrington, the former Foreign Secretary, who led the negotiations that brought white rule in Rhodesia to an end, paving the way for the birth of Zimbabwe, said that the African Union was the ideal organisation to deal with President Mugabe.

Lord Ashdown pointed to action taken by the African Union in March when 400 troops from Tanzania and Sudan landed in the rebel-held island of Anjouan in the Indian Ocean – part of the three-island Union of the Comoros – and ousted Mohamed Bacar, who had seized power in a 2001 coup and who held flawed elections last year.

Lord Carrington said: “Any military intervention by the British would be regarded – not just by Zimbabwe but by all the neighbouring African countries – as a return to colonisation. The real solution lies with the Africans themselves and there are signs that neighbouring countries are getting worried.”

When asked yesterday about possible British military intervention Lord Malloch-Brown, the Foreign Office Minister, said: “It’s not a plausible course and would not enjoy international support. I have not heard anyone here or in any other capital suggest military action is a solution.”

Major-General Julian Thompson, who commanded 3 Commando Brigade Royal Marines in the Falklands conflict in 1982, said action against the Zimbabwe military would be relatively straightforward, but the problem would be getting the troops there.

He said: “I think the Zimbabwean Army and police force would collapse and the population would treat an intervention force as liberators – but would any of the neighbouring African countries give us flying rights over their territory?”

Referring to Ian Smith’s Unilateral Declaration of Independence in Rhodesia in 1965, he said that the colonial powers in the region at the time had refused Britain flying rights – “and today it would be Zimbabwe’s neighbours who would turn us down”.

The former Royal Marine added: “Even if it was decided to use, say, Mozambique’s airspace without permission to reach Zimbabwe, what would the mission be? Would it be to kill Mugabe or put him in prison? – and what about all the generals who support him, what would happen to them? These are the sort of questions the Chief of the Defence Staff would ask if he was given an order from Gordon Brown to send troops to Zimbabwe.

“I think military intervention is morally justified, but we won’t do it because Mugabe keeps on saying that British colonialists are behind the trouble. So if we took part it would be seen as a self-fulfilling prophesy,” he added.

Any involvement by British troops would place further strain on the Armed Forces. Two of the principal go-anywhere brigades are already committed. The 2nd Battalion and the 3rd Battalion of The Parachute Regiment, part of 16 Air Assault Brigade, are serving in Afghanistan, and 3 Commando Brigade Royal Marines takes over in Afghanistan in the autumn.

Harare’s armed forces

25,000 Army personnel

4,000 Air force

21,800 Paramilitary

£79 million 2006 defence budget

3.8% Military expenditure as a percentage of GDP (2006)

45 Number of combat-capable aircraft

40 Number of main battle tanks, mostly nonoperational

80 Armoured infantry fighting vehicles

85 Number of armoured personnel carriers

242 Number of artillery pieces

18-24 Years of age for compulsory military service Sourcesthe Military Balance 2008, IISS; CIA World Factbook

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