Image copyright PA Image caption Debenhams in Luton was one of three stores targeted

Scotland Yard is reinvestigating a 1987 firebomb attack after an allegation it was planted by a member of an undercover police unit.

In a statement, the Metropolitan Police said it was pursuing lines of inquiry linked to the incident at a Debenhams department store in north London.

It said new evidence had emerged during a review of undercover operations.

In 2012 an MP used parliamentary privilege to allege that an officer had planted the device in north London.

The announcement by the Metropolitan Police is one of the most significant developments since allegations of wrongdoing first emerged against the force's now disbanded Special Demonstration Squad (SDS).

The SDS, shut down in 2008, was a secret team inside Special Branch which was tasked with infiltrating political protest groups and activists associated with a range of left-wing or alternative causes, including animal rights campaigners.

Scotland Yard said detectives had reopened the file into the incident in Harrow on 11 July 1987 which was believed to be linked to an anti-fur campaign.

"A team is now pursuing a number of lines of enquiry which were identified following a thematic review of the original investigation, by the then bomb squad," said the force.

"This will include exploiting potential advances in DNA techniques, new information that has been established by Operation Herne [the internal police investigation into historical undercover policing] and claims made under parliamentary privilege by an MP in 2012."

In 2012, Green Party MP Caroline Lucas, speaking in Parliament, said that Geoff Sheppard, one of the activists convicted in relation to the incident had named a former senior SDS officer as being behind the attack.

Image copyright Courtesy Gaurdian Newspaper Image caption Bob Lambert: Former undercover officer

Ms Lucas said Mr Sheppard alleged that Bob Lambert had planted the device after he had been deployed undercover.

The former officer, whose time undercover investigating the Animal Liberation Front is not disputed, has vehemently denied playing any part in the bombing.

"I did not commit serious crime such as planting an incendiary device at the [Debenhams] Harrow store," Mr Lambert said in 2012.

Mr Sheppard and a second man, Andrew Clarke, launched appeals against their convictions in 2014.

The Scotland Yard statement said that the reinvestigation was being led by a senior detective from the Directorate of Professional Standards, the arm of the force that looks into allegations made against police officers.

"As with all ongoing investigations we are not prepared to give a running commentary on its progress, nor to identify who may or may not be subject of the investigation.

"The MPS has made the public inquiry into undercover policing aware of this re-investigation."

The attack in Harrow, north-west London, caused £340,000 of damage and was part of a series of attacks that also targeted stores in Romford and Luton. In all Debenhams lost £8m in relation to the incidents and stopped selling furs.