I have a full time job and also an additional part time job, both of which I pay income tax on. I have just received the P60 for the part time job and we believe I may be entitled to some sort of rebate due to overpayment. How and when would I find out if this is the case and if so, how would the money be returned to me?
Telephone your local tax office and discuss it with them - they will send out the relevant forms.
You are aware that you pay income tax on the whole of your part time salary at either 20% or 40% as your allowances would be used for your main salary.
If you have a conventional Tax Coding on your normal job (something like 522L, say) and a BR tax code on your part-time job then you are very likely to have been taxed correctly.