He bought a country house in his
The multi-millionaire, supposedly heading Tory clean-up efforts, designated it his "second home" for Commons expenses.
But he didn't take out his £271,000 mortgage on the property until 2004 - since when he has claimed more than £63,000 for interest.
Shadow chancellor George Osborne is already under inquiry over the same issue.
Now, Labour MP John Mann has asked Parliamentary Standards Commissioner John Lyon to look into
A spokeswoman for Mr Duncan, who, like Mr Osborne, insists he has done nothing wrong, said the mortgage was always for his constituency home even though it was originally taken out on his