I would suggest that if you are looking at employing staff, then you get professional advice, go to somewhere like Business Link or Entrust, they run free courses on employing staff. They will take you through P45's, P46's, P35's, etc, etc also employee and employer entitlements.
The last thing you want to be doing wrong is upsetting the Inland revenue.
Also go down to PC World and pick up a copy of one of the Payroll and accountancy software packages they have. They all provide a free advice line for the first year and you get updates every April so you are kept up to date with changes to allowances and calculations. They cost about £100 - £150 and much easier than trying to do it with pen and paper.
We use Quickbooks and it literally takes a few minutes each week to do the payroll.
Remember when you employ staff, you need to take into account your Employer NI contributions (around 8%, but will vary depending on personal allowances), holiday pay allowance (again around 8%), sick pay allowance (3% ish)
So if you are going to pay someone £10.00 /hour, then it will actually cost you around £11.90 / hour throughout the year.
I say again seek professional advice!