Shadow Defence Secretary Jim Murphy increased the pressure on Dr Fox last night by accusing him of not telling the truth about a highly sensitive meeting in Dubai organised by his best man and former flatmate Adam Werritty.
And today the minister came under even further scrutiny after the discovery of video footage that shows him and Werritty meeting with the president of Sri Lanka in a London hotel last year - despite his prior claims that his close friend never attended formal meetings with overseas dignitaries.
Mr Murphy says Dr Fox gave him a personal assurance that the Dubai meeting, where the Defence Secretary discussed a potential arms deal, was all above board and that a Ministry of Defence mandarin had been present.
But Mr Murphy says he was shocked to discover later that Dr Fox misled him: the meeting was brokered and attended by Mr Werritty - and no MoD officials were present. And it comes as video footage from a Sri Lankan news channel appears to show Werritty shaking hands with President Mahinda Rajapaksa, who has been accused of war crimes during the country's civil war, during a meeting at the Dorchester Hotel in early December.
The footage shows Werritty was apparently part of Fox's delegation and is present as Fox discusses ongoing peace talks with the Tamil Tigers rebel group. The video was handed to the Observer newspaper by an Italian blogger Nomfup and two separate sources have verified that it is Werritty in the film.