MPs are facing the prospect of further payment demands after it was revealed the expenses claims of 27 of them are being investigated by the tax authorities.

The inquiries were initiated by HM Revenue and Customs after it intensified checks on politicians' financial affairs in the wake of the revelations of Westminster pay and perks.

Any found to have claimed for non-essential items could be billed for 40 per cent of the value plus interest and potentially face fines.

Controversy has also surrounded MPs' failure to pay capital gains tax on the sale of second homes.

"An inquiry does not necessarily mean that there is a problem. Most inquiries are closed quickly," an HMRC spokeswoman said.

News of the investigations emerged as Commons Speaker John Bercow urged MPs to pay back whatever sums were demanded from them by the audit of expenses being carried out by Sir Thomas Legg.

Mr Bercow has himself paid back almost £1,000 after a letter from Sir Thomas earlier this week alerted him to the fact that he had overclaimed allowances on the mortgage for his second home.