The Ministry of Defence has admitted for the first time some details of seven politically sensitive accidents involving British nuclear weapons.

But the MoD conceded that the information released was limited, provoking accusations of a continuing cover-up.

In one accident, a torpedo was dropped on top of a nuclear weapon on HMS Tiger which was anchored off Valetta harbour, Malta.

If the torpedo had exploded or caused a fire, it could have detonated the high explosive within the nuclear weapon, scattering radioactive debris for several miles around, said Shaun Gregory, a Bradford University academic who has studied the hazards of nuclear accidents.

The Maltese government, whose relations with Britain were then strained somewhat, was not told about the accident in February 1974. The Guardian understands that a hoist carrying the torpedo on board collapsed, sending it clattering on to the nuclear weapon.

According to one sailor, two crew members were injured. An official inquiry criticised crew training and the design of the hoist.

The ministry has only admitted a "handling incident" involving a nuclear weapon, which produced "some scratching of protective material."

There was another "handling incident involving a Polaris missile" at a nuclear weapons depot at Coulport, Argyll and Bute, in August 1977.

According to leaks from military sources, the Polaris missile was dropped while being hoisted on to a submarine.

Military convoys carrying nuclear weapons on British roads were involved in three crashes - in Wiltshire in January 1987, on the M8 near Glasgow in August 1983, and near the Coulport depot in April 1973.

The ministry also disclosed that the protective casing around Polaris missiles was "compressed" on two occasions, in 1981 and 1974, on board submarines at sea, but gave no other details.

The carefully worded list has been published following pressure from the Guardian, which requested the information more than three years ago under the open government code.

The MoD decided that full descriptions of the accidents could not be released to protect the operational security of the weapons, but some information could be disclosed to allay public worries.

The ministry insisted that the accidents had not endangered public safety since none of the weapons was damaged or leaked radioactive material.

But the MoD has refused to give any details of other mishaps because they did not "involve any threat to public safety".

An inquiry by the then MoD chief scientific adviser, Ronald Oxburgh, in 1992 found that since 1960 there had been around 20 mishaps.

Nigel Chamberlain, a spokesman for the Campaign for Nuclear Disarmament, said: "Any relaxation of secrecy is to be welcomed, but it has been nine years since the Oxburgh report, and the MoD still has much ground to make up on this front.

"If public safety was their major concern, they would stop sending unmarked nuclear warhead convoys out on our congested roads".

The list confirms for the first time the speculation surrounding the well publicised 1987 accident in Wiltshire, when a 20 tonne MoD truck carrying nuclear weapons skidded off an icy road and turned over.

Armed troops sealed off the crash site and stopped peace campaigners from approaching.