Adam Werritty has played a big part in the life of Defence Secretary Liam Fox – his best man, a former flatmate and a one-time business partner.
Now, Mr Fox finds questions around their working relationship have put his cabinet job in jeopardy.
The personal and business ties between the two run deep.
They first met in the late 1990s when Mr Fox was an opposition spokesman on Scotland and Mr Werritty was studying public policy at Edinburgh University.
Their friendship grew, despite a 16-year age gap, around a shared interest in politics and the US.
In 2005, Fife-born Mr Werritty was by Mr Fox’s side when he married Jesme Baird at a Westminster church.
He was also director of Atlantic Bridge, a charity founded by Mr Fox to promote economic and cultural links between the US and UK, which was dissolved last month.
More recently he has accompanied the defence secretary on a series of foreign trips, at private events and apparently brokered meetings, despite neither working for the government nor the Conservative party.
Mr Werritty, 34, who lives in London and is not thought to be married, presented himself as an official adviser to the defence secretary.
He carried business cards embossed with parliament’s portcullis logo and described himself as an "adviser to the Rt Hon Dr Fox MP".
The Times claimed this self-styled role went as far as having a reputation among lobbyists as the "go-to guy" for gaining access to the defence secretary.
Mr Werritty, who has run health and defence-related businesses in the past, also visited Mr Fox’s office at the Ministry of Defence 14 times in a year-and-a-half – which prompted Labour to call for an inquiry into whether national security had been breached.
‘Perfectly reasonable’
Some of the key claims being made against Mr Werritty include arranging a meeting between Mr Fox and businessmen in Dubai in June, when the defence secretary was on his way home from a visit to Afghanistan.
Mr Werritty was also pictured at a lecture given by the defence secretary in Sri Lanka in July – the MoD said he was "not part of Mr Fox’s delegation and he did not attend any official meetings".
Mr Fox admitted attending a "private event" organised by Mr Werritty and the widow of the Tamil Sri Lankan foreign minister Lakshman Kadirgamar who was shot dead in 2005.
Mr Fox has had an interest in Sri Lanka since his efforts to broker a ceasefire in the conflict when he was a junior Foreign Office minister in 1996.
He said he had a long history of trying to co-ordinate peace efforts in Sri Lanka and that was a "perfectly reasonable thing to do".
It also emerged on Sunday that Mr Werritty attended a meeting between the Sri Lankan president Mahinda Rajapaksa and Mr Fox in a London hotel last year.
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