11 workers at Tihange nuclear power plant have had their passes revoked

May have detonated at plant or gained entry to get 'dirty bomb' materials

The Brussels terrorists may have been plotting to make a radioactive bomb after it emerged 11 nuclear power plant workers have had their site access revoked amid fears of 'insider help'.

Jihadi brothers Khalid and Ibrahim el-Bakraoui had secretly filmed the daily routine of Belgium's nuclear programme chief, before they blew themselves up at Brussels airport and on a Metro train.

It is thought the brothers' spying operation was possible preparation for a kidnap plot to force him to let them into one of Belgium's two atomic facilities. However, it is likely they switched targets to the less well-guarded airport and Maelbeek Metro station after authorities became suspicious.

The terror cell responsible for the Paris and Brussels attacks was planning to attack an unidentified nuclear power station or try and steal materials from it for a 'dirty bomb'. Pictured is the power plant in Doel, Belgium

It emerged last night that 11 workers at the Tihange nuclear power plant, 40 miles south-east of Brussels, have had their access badges withdrawn – leading to speculation the bombers may have been seeking insider help.

Seven of the passes were withdrawn last week, and last Friday additional soldiers were deployed to protect the plant, which has three reactors.

If the terrorists had struck there, it could have caused a catastrophe. The plant lies in a heavily populated area about 50 miles from each of Belgium's borders with Germany, France, the Netherlands and Luxembourg. One Belgian plant is only 90 miles from Kent.

Alternatively, the brothers could have been plotting to steal nuclear material to make a dirty bomb.

Claude Moniquet, who investigates threats to Europe's nuclear sector, told NBC News: 'The terrorist cell naively believed they could use him to penetrate a lab to obtain nuclear material to make a dirty bomb.'

The heightened security at the facility, and the police raids on ISIS boltholes last week which led to the capture of Paris terrorist Salah Abdeslam, may have prompted the bombers to switch their targets to Brussels airport and Metro station, where they killed 31 people and injured 270 others on Tuesday.

Belgium's La Derniere Heure newspaper quoted a police source as saying the el-Bakraoui brothers had hidden cameras in bushes outside the home of the head of the country's nuclear research and development programme.

A Belgian prosecutor refused to divulge the individual's identity 'for obvious security reasons'.

Belgium's federal agency for nuclear control stressed the importance of not revealing the name of the person involved so as 'not to endanger the enquiry or nuclear security' or indeed the person involved and their family.

Belgian bomber Ibrahim El Bakraoui (centre) and explosives expert Najim Laachraou (left) killed 14 at Brussels airport. Their accomplice - the 'Man in White' (right) - fled the airport and remains on the run

Brussels bombers: Khalid El Bakraoui (left), Ibrahim El Bakraoui (centre) and explosives expert Najim Laachraoui (right) detonated bombs at the airport and metro on Tuesday, killing 31 and injuring hundreds more

The footage was found in December during a police raid in Brussels linked to the Paris attacks a month earlier. The filming confounded investigators at first because it showed the entrance to the director's home in Flanders, an area outside the capital.

But after watching all 12 hours' worth of footage, detectives drew the chilling conclusion that the fanatics were trying to gain access to an atomic facility.

Armed troops were sent to defend French and Belgian nuclear facilities following the discovery and both countries' nuclear programmes were put on the highest state of alert.

On February 17, Belgian prosecutors confirmed the existence of the video seized in December. At the time, investigators knew the video camera had been removed by two men, who left the area in a vehicle with the lights off, but did not know their identity.

La Derniere Heure said it was now clear it was the two brothers.

'They rushed their operations because they felt under pressure,' the police source told the paper.

'Even if one couldn't prevent these (Brussels) attacks, one can say that their magnitude could have been much bigger if the terrorists had been able to implement their original plan and not opted for easier targets.'

Tihange nuclear power plant is about an hour's drive away from the Belgian capital where the attacks occurred

The key figure in the alleged 'dirty bomb' plot is Mohammed Bakkali, 28, from Brussels, who was arrested on suspicion of helping to plan the Paris massacre in November.

The video footage of the nuclear power plant director is believed to have been found during a raid at his flat. He is due to appear in court at the end of the month.

Meanwhile, Paris jihadi Abdeslam, 26, said he 'didn't know anything' about the latest attacks, a court in Brussels was told yesterday. He wanted 'to return to France as quickly as possible' to 'explain himself' in a criminal trial, his lawyer said.