David Cameron has ordered an inquiry into whether Conservative Party co-chairman Baroness Warsi breached the ministerial code when she was accompanied by a business partner on an official visit to Pakistan.
The Prime Minister called in Sir Alex Allan, his independent adviser on ministerial interests, to investigate after she admitted failing to disclose her business relationship with Abid Hussain.
Lady Warsi wrote a letter of apology to Mr Cameron, saying she was "sincerely sorry" for the embarrassment to the Government. The Cabinet minister is facing mounting difficulties, with the prospect of a sleaze inquiry into separate allegations about her House of Lords expenses claims, into which Labour are demanding a criminal investigation.
Mr Cameron's referral of her relationship with Mr Hussain to his adviser on the ministerial code comes despite his steadfast refusal to order a similar inquiry into Culture Secretary Jeremy Hunt, who has faced weeks of heavy criticism for his contacts with News Corporation over its attempts to take full control of BSkyB.
Labour said the Prime Minister's actions underlined that he was "bending over backwards" to defend Mr Hunt.
Mr Hussain attended Lady Warsi's July 2010 visit to Pakistan - soon after she had joined the coalition Cabinet. They were both directors of a company called Rupert's Recipes.
In her letter to the Prime Minister, she said "community activist" Mr Hussain was among a number of members of the Pakistani diaspora in the UK who had assisted the British High Commission with outreach events in Pakistan in July 2010.
Although it was "widely known" that he was her husband's second cousin, she said, she had not realised the need to declare that they also had "a common business interest as minority shareholders in a small food company".
Lady Warsi stressed that it was not a trade-related visit and Mr Hussain "did not gain any financial or business advantage" from his involvement, he was not part of the official delegation and no aspect of his visit was funded by the Government.
The Prime Minister said he accepted her apology but was asking Sir Alex to "consider the issues that have been raised with respect to the Ministerial Code and to provide advice to me as rapidly as possible".