Just an additional thought, Mosesg:
I hope that you're not telling HMRC that you're self-employed. You're not!
If you've set up a limited company you're now an employee of that company (as well as being its owner and director). You must (in your role as 'employer') get hold of the paperwork for deducting PAYE and National Insurance from your 'employee' (i.e. youreslf). You can't just pay the (lower) self-employed National Insurance contributions. You (as an individual) must pay the employee's NICs while, at the same time your company must pay the employer's NICs. If you get it wrong you could be hit with a very big bill at the end of the tax year!
This isn't written purely from 'theory'. I used to operate a one-man business (drafting wills), which was run as a limited company. HMRC actually sent me (three times!) the paperwork in relation to self-employment before I managed to get it through to them that, as the director of a limited company, the law regarded me as an employee and not as self-employed!