HM Revenue & Customs have agreed industry wide allowances against income tax for uniformed flight deck crew. They apply to all crew, are not company specific and can be claimed without submitting receipts or proving expenditure.
Applicable to all are two allowances. The first is known as Flat Rate Expense (FRE), and covers likely expenditure necessary in performing your function as a member of flight deck crew. The second covers travelling expenses to certain regular, specific activities such as medicals, sim checks, SEP, amongst others.
Details of each can be found at:
Further allowance can be claimed if you have to provide your own uniform (renewal not initial issue) or noise cancelling headset.
Details again can be found at: