The use of entrapment in the media is not a straightforward subject, though I share the view of most journalists that the end result usually justifies the means.

Going undercover to expose frauds and hypocrites is good journalistic practice. I admire those who do it successfully.

That is not to say that entrapment should be approved lightly - or that it does not present dangers.

I have some sympathy with the view that democracy could be damaged if politicians are hounded so much that they are terrified to speak their minds to anyone for fear of a secret tape recording.

On the other hand, we want politicians who are quite simply honest, both in private and public.

The curious aspect of Vince Cable's entrapment is that the Daily Telegraph chose not to go public with the most newsworthy aspect of his unguarded comments - that he had "declared war" on Rupert Murdoch over his bid to buy BSkyB.

The suggestion that he could bring down the coalition Government if he resigned, and that he felt the Government was cutting too deep and too fast, were interesting enough, though not hugely surprising.

No, the real public interest - the real end result to justify the means - was that the man given absolute power to dispassionately decide whether Murdoch's takeover should go ahead had a bloody big axe to grind.

Once it was clear that he had a personal antagonism towards Murdoch, that power had to be taken away.

That was the bit which really made the entrapment worthwhile and yet the Daily Telegraph overlooked it.

I find it very hard to swallow the claim that editorial judgement, and not commercial considerations, was behind that decision.