I imagine you’ve probably got a BR tax code on your job in the pub, which means you’re having 20% tax taken off your earnings. And a tax code of 747L on your admin job, which means you’re having your entire tax free amount of £7,475 (personal allowance) offset against your £5,000. You are therefore wasting £2,500 of your personal allowance.
I would recommend that you contact HM Revenue & Customs on 0845 300 0627. Make sure you have you have a payslip to hand for each job, so you know your national insurance number and your tax reference. You should ask them to split your personal allowance across your two jobs. This way, your tax codes will be 250L on your job at the pub and 497L on your admin job.
You should then find that you pay less tax overall, because you won’t be wasting any of your personal allowance.
Your local TaxAssist Accountant would be happy to help you get your affairs in order.