Guardian of propriety behind Liam Fox investigation

Among senior politicians and officials working in and around Downing Street, the arrival of Sue Gray in a meeting is not necessarily something to be welcomed.

Not that the middle-aged, quietly spoken official isn't respected – far from it. But if she is called to make the short walk from her desk in the Cabinet Office to No 10 it usually means one thing: the political future of a minister or political adviser hangs in the balance.

When the parliamentary expenses scandal broke it was Ms Gray, director of propriety and ethics, who was charged with examining the returns of ministers to determine who had broken the rules.

It was after Ms Gray had investigated Hazel Blears for failing to pay capital gains tax on the sale of two flats that Gordon Brown described her claims as "totally unacceptable". She was waiting outside the room when Ms Blears complained to the then Prime Minister about his remarks. Ms Blears resigned shortly afterward.

More recently it was Ms Gray who, in the early days of the Coalition, called time on the career of David Laws after she concluded that he had made misleading expenses claims. One person there at the time remembers her judgement: "I think he'll have to go," she said.

Now she is charged with looking into the affairs of Liam Fox and Adam Werritty.

While the final report will be in Sir Gus O'Donnell's name, nobody in Whitehall doubts it will primarily be the work of Ms Gray. She has carried out the interviews with Mr Werritty and others and will make her own recommendations to Sir Gus. What she decides will determine Mr Fox's ministerial career.