It's been confirmed by the high priest of Parliament - Westminster's powers to summon witnesses before its select committees and to punish any accused of telling fibs, are weaker than most people realise.
As the continuing phone-hacking row and, now, the evidence given to the Treasury Committee over interest-rate fixing demonstrate, there is a very real question about what MPs on parliamentary committees can do, when they are not satisfied that they have been told the truth.
This paper by the Clerk of the Commons, Robert Rogers lays bare the threadbare nature of Parliament's powers even to summon witnesses, and the extent to which the sanctions available to MPs are out of date, or inoperable under Human Rights law. He opens with a well-chosen extract from Shakespeare's Henry IV:
Glendower: I can call spirits from the vasty deep.
Hotspur: Why, so can I, or so can any man. But will they come when you do call for them?
Glendower's mystical bravado captures exactly the tone MPs adopt when they talk about the powers and abilities of the "High Court of Parliament". So far no-one has responded with Hotspur's brutal scepticism - but at some point someone, perhaps a banker, perhaps a News International staffer, is bound to do a Hotspur and refuse to play along.
What then? As the paper makes clear, there is no reliable power to compel witnesses to appear before select committees, still less to punish deliberate lies told to them. Even the much-touted solution of requiring witnesses to give evidence on oath, thus making them liable to penalties of perjury, is fraught with problems.
To be sure, the Commons has the power to send the Serjeant at Arms to bring in a reluctant witness - but, as with many of its powers, it now runs the risk of appearing heavy-handed, or worse, plain silly. Picture the Serjeant, in full regalia arriving to apprehend a witness, only to face a stand-off, perhaps on live TV.
Imagine how MPs might appear to the outside world if some offender was brought to the Bar of the House to be admonished - told off - by Mr Speaker; who, by tradition, dons a black tricorn hat for such occasions (which dates that whole procedure a bit). It last happened to the journalist John Junor in 1956 - and, as Mr Rogers says, the Commons might look like a lynch mob if it tried that now. And then, in this non-deferential age, there's always the possibility that the victim might seize the moment and answer back - with the whole incident an instant sensation on You Tube. Remember how George Galloway thundered back at a US Senate committee.
There's some talk of a Privilege Bill to clarify the powers of Parliament; but again, it is far from straightforward to come up with a system of punishing people who refuse to give evidence, or who lie, without giving the courts some jurisdiction over the proceedings of Parliament (a taboo since the Bill of Rights in 1689).
And, as the convoluted process for dealing with the phone hacking witnesses (see earlier post) demonstrates, the handling of these cases has to be fair, allowing "defendants" a real chance to answer the accusations against them and even turn the tables on their accusers.
To be sure, the reputational damage that can be done by a parliamentary hearing may be far more painful than any penalties at MPs' command - ask Rupert Murdoch or G4S. And there are very few incidents where a reluctant witness has not, in the end, appeared before a committee. (The exception is Irene Rosenfeld, CEO of Kraft Foods, who did not agree to appear before the Business, Innovation and Skills Committee in March 2011 to answer questions about the takeover of Cadbury - although other Kraft officials did give evidence.)
Parliament does need the power to compel witnesses to attend, and it does need some sanction when it believes it has been lied to - and these things are surely not impossible to arrange. The US Congress has a robust attitude towards perjury at its hearings, and the Scottish Parliament and Welsh National Assembly both have clearer powers than Westminster. And if we're about to enter into an era of parliamentary investigations of the powerful, in the City, in the media or wherever, clear and robust powers will be essential. But MPs need to be very careful what powers they demand or they could end up sounding like King Lear...
"I shall do such things...What they are yet I know not, but they shall be the terrors of the earth..."