The brother of a 15-year-old who went missing in the late 1970s has told ITV News he is "convinced" the teenager was among the victims abused by members of an alleged historic Westminster paedophile ring.

Detectives have not linked Martin Allen - who disappeared from his home in London in 1979 - to their investigation into claims of abuse at a block of flats near the Houses of Parliament that housed many MPs.

However his brother Kevin Allen told ITV News he believes Martin was "abducted by higher powers" and alleges there has been "a massive cover-up for all these years".

His claims came as detectives announced they are investigating the murders of three young boys as part of their Operation Midland investigation into the alleged paedophile ring at Dolphin Square flats in Pimlico.

Scotland Yard has appealed for witnesses to come forward.

The Metropolitan Police's Det Supt Kenny McDonald said a victim calling himself "Nick" is so far the only victim to contact police and has described abuse that was "pre-arranged, pre-meditated and horrific".

Police said "Nick" alleges he was abused by a group of MPs and other high profile individuals between 1975 and 1984.

The information he has given them relates to the alleged murders of three young boys and police believe that it is "credible and true".

The police refused to be drawn on whether well-known or establishment figures have been named as part of the inquiry, saying only that witnesses had alluded to VIP abuse.

Operation Midland is one of 18 separate ongoing child abuse investigations as part of the over-arching Operation Fairbank.