P N,
UK airline's crew are taxed in a different way to you.
Many airlines in the UK pay an hourly allowance or a meal allowance to top up airline crew's pay. These payments benefit the airlines because they don't include them in their crew's pensionable pay and, because as they are allowances, they carry a tax benefit to the crew also.
The taxman is very aware that these payments are not used solely for paying for food and tax them accordingly, only allowing some of the payments to be tax free.
Every few years, each of the airline's crews have to go through an audit process, where some crew are picked and have to provide receipts for their purchases to justify the tax free element of these allowances. Therefore they would be very interested if they thought some crew were not actually paying for their breakfast. I have to say though that, no hotels that I personally stay in gives free breakfast. Mores the shame!