forensic

Both vehicles, a distinctive beige Nissan Note and a black Volvo XC40 were seized following Monday night's arrests and will be subject to forensic examination, she said.

How it happened has been the subject of deep reporting by journalists, police investigators, forensic specialists, industry safety experts, and a series of criminal and civil court cases.

Detectives had previously said officers discovered a crater at a building site and during follow up searches and further forensic tests showed a military grade explosive was used.

Ms Ayling said forensic evidence found a flammable liquid was "thrown up the stairs, in the hall and in the conservatory", which she argued showed the defendant's motive.

He said the BBC had launched a "forensic analysis" into what had happened.