The admission by Baroness Warsi is a serious blow to the Conservative Party's pledge to be transparent in its dealings, and will increase pressure on Mr Cameron to replace her in a reshuffle. The failure to make a declaration means that the public was unaware that she had another source of income, over and above her salary, which is paid by the Conservative Party, and the £300 a day allowance which she is eligible to claim when she attends the Lords. The baroness updated the register of interests for members of the House of Lords last Monday. It now states under "land and property": "Flat in London NW from which rental income is received." The Prime Minister and Baroness Warsi have spoken of the commitment to transparency by the Conservatives and the Coalition. In November 2010 Mr Cameron said "it is our ambition to be one of the most transparent governments in the world." In July last year the peer said: "This Government is delivering unprecedented transparency." The total amount that she failed to declare is not known because Baroness Warsi did not disclose it last night. Peers are required to register any rental income worth more than £5,000 in a calendar year but do not have to say how much. However, the amount is likely to run into five figures because it involves rental income from a home in London for at least 12 months. As well as raising questions over her own financial affairs, it will further strain relations with grassroots members, among whom the 41-year-old baroness is not believed to enjoy widespread popularity. The political career of her special adviser was also in question last night. The failure to make a declaration emerged from a dispute between Baroness Warsi and a Conservative donor and fund-raiser, Dr Wafik Moustafa. He was upset when the Conservative Arab Network, which he founded, was told earlier this year to sever its links with the party and was subsequently threatened with legal action by Baroness Warsi. That prompted him to disclose that he had given her and her special adviser, Naweed Khan, accommodation in London. In the course of inquiries made because of his public statement, the failure to make a disclosure about her rental income was discovered. Baroness Warsi said last night that she bought a flat in Wembley, north-west London, in September 2007 to use after being ennobled. However, she said that the property transaction was not "due for completion" until 2008 and so she had to find accommodation elsewhere, "predominantly" in two hotels. "Not having made advance bookings for these hotels, there was a period of about six weeks when I spent occasional nights at a flat in Acton, which was occupied by Naweed Khan, at the time a member of Conservative Campaign HQ staff," she said. However, Mr Naweed was actually staying rent-free at Dr Moustafa's home in London, meaning that by extension Baroness Warsi was receiving his hospitality. Baroness Warsi said she moved into the Wembley home in March 2008 and stayed there until June 2010, when "upon security advice, I moved to another address closer to the House of Lords." She said that some months later she began, "with the prior approval of the Cabinet Office and the Leader of the House of Lords, to let out the Wembley property." I repeat: at all times my ownership of the flat and the fact that it was being let out was fully disclosed to Cabinet Office officials and HM Revenue and Customs, and was appropriately reported on the register of Ministers" interests held by the Government." The disclosure means that she failed to declare rental for at least 12 months, and up to 18 months. An average rent for a one-bedroom flat in Wembley is currently £1,000 a month, meaning the amount undeclared could be as high as £18,000. Baroness Warsi has been criticised over her performance as Tory party chairman. Some Conservative MPs want Mr Cameron to replace her with Grant Shapps, the housing minister. Baroness Warsi became the first Muslim woman to be selected as a parliamentary candidate by the Tories, contesting the Dewsbury seat in 2005, but failed to win. This month she said a small minority of Pakistani men saw white women as "third-class citizens" and "fair game" - following a case which saw nine Muslim men found guilty of grooming young white girls for sex.