New evidence has emerged in the case of Binyam Mohamed, a former terror suspect who says he was interrogated and tortured with the complicity of MI5.
Binyam says that he was held in Morocco in 2002-3 and abused by police while there.
Lawyers acting for MI5 have said that MI5 was unaware that Binyam was in Morocco.
But new documents revealed by the high court last week show that an MI5 officer, known as Witness B, visited Morocco three times while Binyam says he was being held there.
Witness B is being investigated by Scotland Yard amid allegations of “possible criminal wrongdoing”.