Re: Why only IT?
If you're worried about having to use engager's kit, Hall v Lorimer (1993 Ct App IIRC) is your friend - as the vision mixer on Have I Got News For You, he was able to successfully rebut* HMRC's argument that using the BBC's 8' wide mixing desk was an indicator that he was an employee. Apparently, in The World According To HMRC(TM) any self respecting self-employed vision mixer owned their own £250k mixing desk and hawked it around the country, from show to show. Thankfully, the Court of Appeal had a slightly closer grasp on reality than HMIT Hall, and we now have a persuasive precedent that actually accords with the world as experienced by normal people. [for anyone who wants to know just _how_ close a grip the senior judiciary keep on reality, the excellent Steve bell cartoon at http://www.belltoons.co.uk/bellworks/index.php/if/1985/1082-0-0-85JUDGESPAYCLAIM should help. nb it's 30 years old now, so the inflation rates are a bit crock)
*I think I've got the right word there, but if it should be refute I apologise. It's late... *checks watch* ... early and I've had a long day. And a glass or two of wine. Sorry; it's the weekend.