MP's Expenses Witnesses To Take An Oath?

Quentin Letts, writing in the Mail, raises an interesting question for when the public, televised hearings into MP's expenses takes place.

He makes the point all that is required is for the hearing to administer the Parliamentary Witnesses Oaths Act 1871. This dusty law permits any Commons committee to administer the oath when hearing evidence. Should an MP then not be truthful they would be liable to be charged with perjury.

As Letts also states, the practice of giving evidence under oath is standard procedure in the USA at congressional committee hearings and if Parliament is determined to 'clean itself' then this must, surely, be a practice to be adopted?