From experience of helping several Thai widows following their husbands/partners death, the the occupational pension paid to a widow or bereaved partner...and children in many cases... is invariably paid without deduction of tax. Only where there is a delay in claiming and arrears mount up, has tax been deducted.
Where tax has been incorrectly deducted details need to be sent to the relvant tax office who will sort matters out (more often than not in the next, not current tax year) and in such cases it
generally requires help from a British subject who knows a little about tax matters
The widow/partner needs to be aware that every year or so, she will receive the equivalent of a Life Certificate. which needs to be completed and returned speedily otherwise pensions are stopped.
Note also, where UK probate is required and a lawyer is involved, if the expat has been overseas for a while, they are regarded as domiciled outside the UK, and VAT on lawyers fees is exempt.