I am retired, have a forces pension which is taxed,have also a retirement pension which takes me over the threshold for claiming benefits, now my question is, is if I take on a part time job of 16 hours per week will I have to pay tax on this, any help please.
You will have to pay tax on all of your income that's over the Personal Tax Allowance for your age.
If you're under 65 the limit is £9,440 per year, over 65 it's £10,500 or over 75 it's £10,660. So if your total income is under these limits, you shouldn't be paying any tax at all.
^ dasherman's said what I was going to. You should only be paying tax if your total income from pensions and paid work takes you over the tax-free allowance.