From a lawyer, just before the Murdochs appeared at the committee:
Some people must be wondering whether the evidence will be given on oath. That’s very unusual in select committee hearings, but the chairman does have power to administer an oath. I very much doubt he will, though, since it makes little difference. If a witness lies under oath in the committee, he or she will be guilty of perjury – but that perjury would be punishable only by the House of Commons, not in the courts. If he or she lies not under oath, that would surely amount to contempt of Parliament – again, punishable by the House. In either case, the punishments available would be the same.
...
Sir George Young, Leader of the House, said last week that the Committee on Standards and Privileges (to which any refusal to answer questions would be referred) could fine a witness; Chris Bryant, the Labour MP, said that was “wrong”. According to Erskine May, Parliament has seemed to accept for some time that it cannot impose fines (unlike the House of Lords, oddly), based on non-binding judicial statements (obiter dicta, in legal jargon) in a couple of 18th century cases that said the Commons is not a “court of record”. A number of Parliamentary committees since the 1960s have recommended that Parliament legislate to put the power to fine beyond doubt – but it never has. It ought to do so now as a matter of urgency.
What’s not in doubt is the House’s power to imprison someone for contempt – though only until the end of the Parliament, according to Lord Chief Justice Denman in Stockdale v Hansard back in 1839. That limitation might, one day, prove very important: if someone were imprisoned against the background of a major national scandal that forced a general election, he or she would have to be released soon after the election was called. Parliament hasn’t actually imprisoned anyone since 1880, as it happens. I detect, though, in recent years, an increasing assertiveness – or arrogance – from MPs; I’m certainly not making any sort of prediction about this case, but I would not entirely exclude the possibility of Parliament’s seriously making the threat of imprisonment again before long.
http://www.headoflegal.com/2011/07/19/the-select-committee-the-murdochs-and-brooks/That's what
potentially could be done; reading
the Commons factsheet on the penal powers of the house (linked to via the
New Statesman column the first link mentions; the writer is a lawyer who also blogs as 'Jack of Kent', and is pretty good - worth going to if you want to find out about libel reform in the UK) it seems it's been rarely used recently for non-members. For the Murdochs, I would think that their biggest problem could be that misleading Parliament like that could well make them seem not 'fit and proper' to keep their 39% stake in BSkyB.