Witney MP and Conservative leader David Cameron has been urged to explain why he paid off a mortgage on his London house rather than his taxpayer-funded constituency home.

Mr Cameron paid off the £75,000 he owed on his Kensington property from his own money, just months after taking out a £350,000 mortgage on his home in Dean, West Oxfordshire.

His actions did not break any rules, but a national newspaper calculated that if he had paid the £75,000 towards his Dean home, it could have saved the taxpayer as much as £22,000.

Last night the chief executive of the TaxPayers’ Alliance, Matthew Elliott said: “He has done the right thing by publishing information about his expenses but he should explain why he took this course.”

A party spokesman said even if Mr Cameron had reduced his Dean house mortgage, he would have been entitled to claim exactly the same amount, and the cost to the taxpayer would have been exactly the same.