I paid myself from my company last year but did not issue myself a P60 with we closed the company back in December 2010. It's now time to do my tax return, and I am unsure what the exact figures of total pay/tax deducted were, are there any tools/companies that could work out the values on a P60 from the net pay?
Your P60 is just a statement of Tax and NI paid for that respective tax year - nothing to do with net pay. If you have payslips (which you should, as employers have a legal responsibility to issue them on or before pay day) then your P60 figures will be the same as your latest dated payslip on or prior to 5th April
P60s are only issued to employees of a company where the employee is in active employment as at 5th April, if you don't have a P60 due to not meeting this criteria then you can use a statement of earnings or a P45 to get your Tax and NI YTD figures.
When you closed your company you should have issued yourself a P45, if you weren't in employment for the rest of that tax year, then you need to use that for your self-assesment