We would not just put any document in the public domain

MoD spokesman

Shadow defence secretary Bernard Jenkin criticised such a move as a "monstrous free gift to terrorists" and called for an immediate government investigation.

He told BBC News Online: "The fact that this information has been lying in the public records office is extraordinary.

"Such information may already be in the public domain, but why needlessly help rogue states and terrorist organisations with such comprehensive instructions on how to make an atom bomb?

"I will be pressing the government for a comprehensive explanation."

Stringent review

As a result of the outcry, a spokesman for the MoD said it had sent someone along to the Public Record Office to check the content of the files.

He added: "We have a very stringent review process of all documents and before they are placed on public file they are very carefully checked for any sensitive material.

"We would not just put any document in the public domain."

The files are said to relate to the construction of Blue Danube, the first British atomic bomb, which was built in the late 1940s and early 1950s.

It is also said to describe various ways in which such a bomb could be smuggled into the country.