He has been under pressure after a week of allegations over his working relationship with friend and self-styled adviser Adam Werritty. Mr Fox had denied wrongdoing but admitted he allowed the divide between his personal and professional lives to become \"blurred\". An investigation is under way into Mr Fox\'s conduct and Labour have accused him of breaking the ministeral code. Liam Fox became the first of Cameron\'s Conservative cabinet ministers to leave in the 17-month life of the coalition and now triggers the prime minister\'s first reshuffle, an operation he had wanted to hold out doing until half way through the parliament. It is expected Cameron will perform a limited reshuffle, merely replacing Fox without going reorganising his entire government line-up. Fox is said to have crumpled under the weight of this week\'s revelations and the prospect of another weekend of speculation He could not hold out until the inquiry into his behaviour wound up officially – expected to be at some point next week. The prime minister had always held out the right to exercise his own judgment and keep Fox in his post even if O\'Donnell\'s report had been critical, but the defence secretary decided to short-circuit the process and limit the personal and political damage. It is understood that Werritty\'s appearance before Sir Gus O\'Donnell – the man performing the inquiry to establish the propriety of his work – did not impress the cabinet secretary. Fox will now join the backbenches where he enjoys some popularity but it is not expected he will act as a lightning rod for discontent.