EIM71200 | Tax treatment of waiters: tips, etc.
From HM Revenue & Customs · Employment Income Manual
Tips paid to waiters and others working in hotels, restaurants, clubs, etc. are earnings that are chargeable to tax in addition to normal wages (see EIM07900).
As regards coding, see guidance in the PAYE Online Manual (POM) - search for “Tips, Gratuities, Service Charges And Troncs”.