Security is being tightened in London, amid fears of a campaign by dissident Republicans in the wake of a rocket attack on MI6 headquarters, last night. Security chiefs believe the Real IRA was behind the attack on the top-security building on the south bank of the Thames in central London.

Earlier tonight police investigating last night's attack on the headquarters of Britain's Secret Service found part of a rocket launcher. Scotland Yard said that the discovery was made in a park in Vauxhall Cross, central London, near the MI6 building which was rocked by an explosion last night. A Metropolitan police spokeswoman said it was not known if the launcher had been fired from the spot where it was found.

Earlier, the head of Britain's anti-terrorist squad said that he believed that a rocket launcher may have been used in last night's attack on the MI6 building. Alan Fry said this morning that it may have been similar to weapons found recently in Northern Ireland and the Republic and which are available in the former Yugoslavia. No one was injured in the attack.

The British Foreign Secretary Robin Cook has said that last night's missile attack on MI6 headquarters in central London did not damage the inside of the building. He said if the attackers' objective had been to disrupt the operation of the secret services, this had failed.

By first light, police were beginning to inspect the damage to the riverside headquarters of Britain's secret intelligence service. A section of an eighth floor window was shattered by a missile fired at the MI6 building shortly before 10pm last night. There was no warning and no one has claimed responsibility. Police sealed off the area to all but the emergency services. There were no injuries, but they had to wait until this morning before they could begin the painstaking task of combing the area for clues. Forensic teams have been searching an area of about 500m around the building. The anti-terrorist branch from Scotland Yard say that they are keeping an open mind on who was responsible, but it could have been an Irish Republican group.

Earlier this year, the Real IRA was thought to have been responsible for two incidents in London, when explosive devices were planted under Hammersmith Bridge and at a railway line. If last night's incident was the Real IRA, it will have been their highest profile target yet.