Former Hove MP Ivor Caplin is one of six politicians who have yet to repay expenses that they were found to have overclaimed.
Mr Caplin, the Labour MP for Hove from 1997 to 2005, is said to owe nearly £18,000 which he claimed for mortgage interest payments in relation to his second home.
The House of Commons authorities described Mr Caplin as one of four former MPs who was refusing to pay.
But Mr Caplin, who served as a Defence Minister for two years under Tony Blair, said that he was co-operating with the authorities.
He was asked to repay £17,865 by Sir Thomas Legg after a review of all claims by MPs since 2004 held in the wake of the expenses scandal.
When the Legg report was published in February, Mr Caplin said that he had not been contacted by Sir Thomas.
The BBC Radio 4 programme The World At One carried a report about money still owed on Thursday.
In a statement to the programme a spokesman for Mr Caplin said: “Mr Caplin has never been given an opportunity to explain the claims he made but welcomes the chance he has recently been given to do so and looks forward to working with the House authorities to resolve this matter.”
Mr Caplin now runs his own business, Ivor Caplin Consultancy, and works for Foresight Consulting, a lobbying company.
Before he became an MP he worked for Legal and General in Hove, served as leader of Hove Borough Council and deputy leader of Brighton and Hove Council.
