It may be expensive and difficult but doesn't the Moyles example illustrate precisely that HMRC are not backing off from the chase? Not letting the big fish go? Moyles is a well-known personality so his case makes the papers. For every Moyles there are probably a few hundred others that we don't hear about, also falling foul of the dodgy scheme, also failing to avoid tax. Big feather in the HMRC cap. Moyles trying to take out an injunction means he's been really badly advised.... secrecy being almost impossible in the Twitter era. Hope he's learned a lesson.
Chris Moyles earned £500k from the telly tax, but didn't want to pay taxes himself, paying a % to a dodgy tax avoidance scheme, which those flogging it claimed meant he had to pay, no, or minimal, tax.
Having failed to avoid tax, he then tried to get an injunction to prevent disclosure of the fact that he decided to sign up to this scam scheme. Thanfully no injunction was granted.
You can see how expensive and difficult it is for HMRC to chase after these scumbags with deep pockets and expensive lawyers. Try not paying a £10k tax bill and they will come down on you. Avoid paying £1m and it will probably cost as much again in legal fees.