Intelligence gathered before the Omagh bombing is to be reviewed after a BBC television documentary claimed that the perpetrators of the deadliest terrorist attack in the history of the Troubles were being monitored.

The Government has asked Sir Peter Gibson, the Intelligence Services Commissioner, to look at all intercept material gathered by the security and intelligence services, and how it was shared.

Panorama claimed that GCHQ, the Government listening post, was recording the Real IRA bombers’ mobile telephone calls before the attack in 1998, which killed 29 people and a pair of unborn twin girls.

The programme said that it had been unable to establish whether the calls were being listened to in “real time” or were recorded for future examination.

Relatives of the victims, who are pursuing a civil action against a number of people whom they accuse of carrying out the attack, said on Tuesday that they would take legal action against the Government within a week unless the recordings were given to them. In spite of a pledge by Tony Blair, then Prime Minister, to leave “no stone unturned” in bringing the guilty to justice, nobody has been successfully prosecuted.

The Cabinet Office announced that Sir Peter would review all phone intercepts relating to the attack. The process will take three months and Gordon Brown will report the outcome to the House of Commons.

Michael Gallagher, whose son Aidan died in the explosion, said: “We welcome the swiftness with which the Government has moved on this. However, we believe that the families should have an input and should be consulted.

“It is indicated that this will take up to three months. We feel that the civil action now taking place, which will be over by that time, is the best possible way of using any intelligence or evidence gleaned from that.

“We would urge Sir Peter to seriously consider making this material and evidence available as soon as possible. If enough resources were applied to this enterprise, we don’t see why this could not be done in a matter of weeks rather than months.”

Mr Gallagher added that all options, including legal action, remained on the table for the campaigners.

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