Hi Xhead, as I understand it, what Atlantic says is not strictly true. If for instance you continue to live in Canada but worked for a UK based company you would be covered by the reciprocal Tax agreement between the two Countries, so long as you paid the Tax due in the UK on the earnings in the UK, you would not have any additional Tax liability in Canada. However, for Seamen working in the UK who spend less than half the year inside the UK 3 mile limit they have no UK income Tax liability on their earnings as a Seamen. If you have other earnings from another job as well, or large amounts of investment income it becomes more complicated.
Best thing to do is talk to someone that has done this.
I also understand that the UK and Canada have reciprocal arrangements for the State Old Age Pension, if you pay UK National Insurance contributions, which would be deducted from your pay automatically by UK employers, these contributions will count towards a Canadian Pension if you retired in Canada and your Canadian contributions would count towards a UK pension if you retired in the UK.
I think you could also make contributions into a UK based, defined contribution Pension scheme ( which all UK employers are required to offer to their employees, if you were working in the UK.
But you definitely need to talk to someone who has done it or an expert on International Seafarers Taxation and Pensions.
I hope this helps.
It is always better to ask a stupid question than to do a stupid thing.