Depends on your age I think, plus you don't have to be working to pay tax it depends how much income you get in total, my dad pays tax and he's nearly 80 his small works pension takes him into the tax bracket, try looking at the yougov web site under tax ( sorry can't get link at the moment for you)
If you are in receipt of any pension, if it takes you over the personal allowance threshold then anything extra earned by you will be taxed: Personal Allowance for people born after 5 April 1948: £10,600
Good luck, my dad worked into his 80's after he fully retired, part-time, so I doubt if he would of paid tax. I couldn't ask him now, as I'm afraid he wouldn't remember.