[Bevdeforges]

I don't know much (i.e. anything) about UK taxes, but one thing to check on is whether or not you are entitled to the personal allowance as a non-resident. It's fairly common for non-residents to have the appropriate taxes deducted from their pensions prior to payment overseas - and in many cases (i.e. depending where the pension is coming from), there is no personal allowance or exemption for a non-resident.
Cheers,
Bev