P11d is a report that HMRC requires to be done annually on Directors' and Employees' Expenses and Benefits. Employers have to file a report declaring the expenses and benefits provided. These benefits are evaluated and both employer and employee are taxed as if they had been paid the equivalent amount through PAYE.

It is designed to close a tax loophole whereby employers could otherwise buy staff perks as part of their remuneration package without these perks being subject to income tax or National Insurance.

For more information see: https://www.gov.uk/employer-reporting-expenses-benefits/reporting-and-paying