You need to take professional advice on this subject. Squawk 6042 is correct but this applies but only for a number of years. After a period the split year treatment option is no longer available and you become taxable for everything earned in that tax year.
To give you a brief background, I am not aircrew, but was working in Qatar for 8 years until being laid off this March. I was already planning to retire next year so I was investigating the HMRC rules to ensure no nasty surprises. According to my UK accountant they are not straightforward and the only way of being certain to avoid being taxed was to spend less than 26 days in the UK in your final tax year.