Conservative Party co-chairman Baroness Warsi has admitted failing to declare rental income in the register of interests for members of the House of Lords.
The Cabinet Office minister said the omission was due to an "oversight", adding that she had reported the letting of her Wembley flat in the Register of Ministers' Interests.
The arrangement had also been declared to the Cabinet Office and HM Revenue and Customs, she said.
The Tory peer bought the property in 2007 but moved closer to Parliament when she became a minister in 2010, after which she began letting the Wembley flat.
"Due to an oversight, for which I take full responsibility, the flat was not included on the Register of Lords' Interests when its value and the rent received came to exceed the thresholds for disclosure," she said.
"When the discrepancy became apparent this week, I immediately informed the Registrar of Lords' Interests of its omission.
"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."