Don't forget, however that trademarking is for those who are worried about people passing themselves off as you. It's not about protecting intellectual copyright on your logo - that can be achieved just as easily by getting your bank manager to stamp and sign a copy of your letterhead.
Also trademarks aren't necessarily universal (either geographic or across markets). If you are considering trademarking I'd suggest you speak to an Intellctual Property legal adviser. (Leeds Business Link offers limited free access to solicitors, maybe your local one does too)