The Reindahlen base was already on alert on Monday before the explosion happened, probably because of Nato concern following the shooting in Rome of General Licio Giorgieri.
Mr John Stanley, armed forces minister, said in the Commons that the higher than usual state of alert had probably saved injuries. There were 'self-evident security difficulties' at the headquarters because the base was sprawling and crossed by several public roads.
Yesterday claims of responsibility for the attack were made in Dublin by the Provisional IRA and in Germany by a previously unheard of group, the National Democratic Front for the Liberation of West Germany .
The German claim was being given little credence by the security forces in Britain and Germany , which accepted that the IRA almost certainly planted the bomb. It exploded only hours after Mrs Thatcher returned to Britain after meeting the German Chancellor Dr Khol.
The IRA, which has mounted several previous attacks on British bases in Europe, has well known connections with European terrorist groups, and could well have been operating with the German Red Army faction.
The West German chief public prosecutor's office in Karlsruhe, which is investigating the attack said there were still no firm clues. A spokesman said of the claim from the National Democratic Front, supposed to be a right-wing organisation: 'We have considerable doubt that this is genuine. '
The IRA claim said that the British forces could consider themselves lucky. The active service unit's brief was to inflict a devastating blow but to avoid civilian casualties. 'Because of the presence of a large number of civilians, including many women, in the immediate area a warning was given. '
The German bomb exploded outside a mess where a party was being held by West German officers and their wives. Only the mess staff, waiters and cooks, were British. Three of the injured were still in hospital last night, being treated for minor injuries caused by flying glass.
Yesterday German police with dogs were combing the sealed-off area around the mess where the explosion left a large crater. Parked cars were smashed and windows and doors were blown out of the building.
Mr Stanley said in the Commons that a warning call to the West German Press Association before the attack was not passed on because of language difficulties. The call was in English and spoke of a bomb at Monechengladbach, near the base. Another telephone warning, in German, had been received at Reindahlen a few minutes after the explosion.
The minister said that an internal security investigation would take place. In answer to questions from Labour MPs about the wisdom of employing civilian German staff, who might pass on information to terrorists, Mr Stanley said he had full confidence in the local personnel. West German security and police authorities were cooperating in international efforts against terrorism.
The SDP spokesman, Mr John Cartwright, had asked if there was enough international cooperation against terrorist groups attacking Nato, in the light of the Italian shooting.