A public inquiry has heard that Britain's domestic counter-intelligence and security agency, MI5, did not reopen its investigation into the Manchester Arena bomber, Salman Abedi, despite knowing he was visiting a convicted terror offender in prison.

The probe is to examine whether Abedi's attack, which killed 22 people and injured hundreds on 22 May 2017, could have been prevented. On Wednesday, the third day of the public inquiry heard that signs of Abedi's radicalisation went back several years.

MI5 had received information on Abedi dating back to 2010. However, it repeatedly assessed that he did not pose a security threat despite knowing of his contact with ISIS supporters. Paul Greaney QC, counsel to the inquiry, said it would consider whether it was "reasonable" for MI5 to close an active investigation into Abedi in July 2014, and not to reopen it in the light of new intelligence.

Greaney added: "MI5 information indicated that Abedi visited a terror offender in prison on more than one occasion, but MI5 assessed that this did not justify reopening him as a subject of interest."

"Links with Abdalraouf Abdallah are of significant interest to the inquiry." Greaney said Abedi and Abdallah were in "regular telephone contact" from 2014 onwards, and had "conversed about martyrdom".

Abedi travelled to HMP Belmarsh, a Category-A men's prison in Thamesmead, south-east London, to visit Abdallah while he was being held on remand in 2015, then visited him in Liverpool's HMP Altcourse in January 2017.

The following month, officers at the private G4S-run jail found that Abdallah had an illegal mobile phone in his cell, which showed calls to Abedi's number. Abdallah, who is still serving his sentence, has refused to answer questions from the public inquiry.

Greaney said "considerable efforts" were being made to obtain evidence from him, adding: "We wish to understand if Abdallah had any role to play in the development of Abedi's worldview." He added: the inquiry had commissioned a report on radicalisation inside British prisons, asking: "How was Abedi able to visit a prisoner such as Abdallah?"

"MI5 assessed there was nothing to indicate he posed a risk," Greaney said.

On 22 May 2017, Salman Abedi detonated a shrapnel-laden homemade bomb as people were leaving the Manchester Arena following a concert by US singer Ariana Grande. 22 People died instantly including children and parents.

ISIS claimed Abedi as one of their soldiers..