You will need to check on the documentation which comes through when you've registered as to exactly what you can claim off the salary - percentages of phone bill etc. You can work your own accounts monthly but they work on an annual tax return. If you submit the return before September they'll calculate the tax you owe for you. If you miss that you've got until the end of January to get it in before risking a fine.

All this will be in the form mate - you might as well register it yourself for free and then go from there. If you decide to get an accountant afterwards then you can, but I doubt you'll need to.

Cheers,

Andy

P.S. Register AFTER you've cleared it with your boss, as you can't be self employed and employed by someone at the same time (or something along those lines anyway).