Secret letters sent to on-the-run suspects in Northern Ireland did not amount to immunity, exemption or amnesty from arrest, the UK Government has said.

Details of the documents emerged after the Old Bailey trial of John Downey, who denied killing four soldiers in the 1982 IRA bombing of London's Hyde Park, collapsed.

He was one of 187 people who received letters assuring them they did not face arrest and prosecution for terror crimes under the Good Friday Agreement.

Northern Ireland spokeswoman Baroness Randerson told the Lords yesterday: "No recipient of such a letter should be in any doubt that if evidence emerges after the date the letter was issued in connection with terrorist offences committed before the Belfast agreement, they will be liable for arrest and prosecution."

But former Ulster Unionist now independent crossbencher Lord Maginnis of Drumglass said they were "free to come back without interference from police".