It depends on the company. Doesn't easyJet say something like: "You don't have to wear a suit but if you feel more comfortable if you do we won't hold it against you".
I think Dani hits it on the head with the suit/shirt/tie advise (especially the bit about cartoon ties, don't do it. I'd leave the Disney socks at home as well). It is difficult to be overdressed, but easy to be underdressed. You can always take the jacket off if the suit turns out to be OTT.
Whatever you wear, make sure your shoes are up to scratch. A nice suit with hush puppies is a waste of a nice suit.
Read that Irv something book a while ago. Way too American for use in the UK. I wouldn't use his CV templates either, they look horrible. Maybe the old septics like it that way though.
Good luck