The Cabinet minister asked Paul Kernaghan to look into accusations she claimed for accommodation while staying at a friend’s house rent free.
Prime Minister David Cameron backed Lady Warsi, who insisted her expenses claims were “both in accordance with the law and the spirit of the rules”.
Mr Kernaghan will carry out “a preliminary assessment” before deciding the next course of action. Lady Warsi said she would co-operate with any inquiry, but declined to answer questions over whether she would resign over the row.
Speaking during a visit to Malaysia, she said: “I take these allegations very seriously; it’s why I said right at the outset that I would fully co-operate with any investigation. I believe that being a member of the House of Lords is a privilege. I take that privilege seriously.”
Mr Kernaghan was invited to investigate allegations which surfaced over the weekend. The row broke out when Lady Warsi insisted she made an “appropriate payment” to her friend, Tory official Naweed Khan, who is now one of her aides, for the nights she stayed at the property in Acton, west London.
Mr Khan released a statement saying she made a payment each time she stayed. But the property’s owner, former Conservative donor Wafik Moustafa, denied receiving any income from either Lady Warsi or Mr Khan.