Per Diems are taxable as are all salaried income. The tax office allows companies to buy employees meals whilst on duty. Most tax offices allow companies to pay a standard amount for meals which the tax office and the company agree can be in lieu of meals being paid for as it is much easier to administer and saves the company a fortune in administration. This standard amount is agreed between the company and their tax office to be tax free to save on administration at both ends. These payments are known as per diems. Some years ago I heard that the UK tax office cancelled all per diem deals as one airline allegedly offered some crew double per diems under some circumstances which amounted to tax free salary bonuses. The tax office then stated that all expenses should be paid on receipt. A per diem scheme was then introduced for all businesses which is UK meals are paid for on receipt and per diems are allowed for travel outside of the UK. The maximum amounts allowable can be found here
https://www.gov.uk/government/public...outside-the-uk
Your company has probably agreed their own deal with HMRC.