I’m EU citizien but not Uk national and pay 20%tax when working in UK waters, is this reclaimable for me.
Anyone working in the UK sector is liable for UK tax, irrespective of nationality or residency. Its pretty much like Norway in that respect. Its were the money is earned that determines if UK tax is due. The exception is SED, which is open for EU residents who pay UK tax from April 2011. The UK has tax agreements with other countries and it may be possible to transfer liability to home your home country.
How its possible to pay a flat rate of 20% I’m not sure. I have however seen South African folks on a similar deal and a flat rate of 20% globally. I can only presume the company takes an "average" tax liability worldwide and applies this monthly. How this is legal is beyond me.
Is the 20% reclaimable? If you qualify for SED then its possible.