How can select committees avoid being misled?

It's pretty rare to make witnesses to Commons select committees swear to tell the truth, but on Monday a civil servant was required to do so by the Public Accounts Committee. Anthony Inglese, one of the most senior lawyers in the civil service was made to swear an oath on an actual Bible, and warned he must tell the truth, the whole truth and nothing but the truth, as the PAC probed the tax deals made between HMRC and big companies including Vodaphone and Goldman Sachs.

Later this week James Murdoch appears before the Culture, Media and Sport Committee - with some MPs concerned about evidence heard in the course of their earlier inquiry into phone hacking. What happens if they decide that is indeed the case?

It is a contempt of Parliament to lie in evidence to a committee - and perjury if the oath has been sworn - and anybody caught telling porkies could be subject to criminal penalty. But it's not clear what. The parliamentary bible, Erskine May, makes it clear that witnesses who "give false evidence, prevaricate, present forged or falsified documents... or attempt in any way to deceive a committee... may be reported to the House and dealt with as determined". But the precedents for such action are ancient indeed - the latest example cited is 1946-7 and another dates back to 1897. And it's really not clear how the Commons would deal with the situation were a liar to be unmasked.

As far as I can make out, the course of action would be for the aggrieved select committee, or perhaps an individual member of it, to seek leave from the Speaker to raise the matter as an issue of parliamentary privilege. Privilege issues take precedence over all other parliamentary business - so, if Mr Speaker agreed, the matter would be debated as first business the next day.

But what, exactly, would they debate? It could be a call for a further investigation - which might mean a reference to the Standards and Privileges Committee. It could be a summons for the offender to the Bar of the House - something last done in 1956 after Sir John Junor, as editor of the Sunday Express, ran a claim that MPs were abusing their petrol rations. Or it could be a motion to punish the offender - Parliament has a theoretical power to jail people for contempt, and the building does contain a cell for this purpose. But a Committee on Parliamentary Privilege in the 60s urged MPs to be extremely careful about exercising such powers.

The fact is, the last time such offences were dealt with, the range of punishments available probably involved hot irons, or possibly transportation to the colonies. MPs will be setting new precedents however they react, if at some future point they do conclude that they have been lied to.