My understanding is that the 5% deduction from the sales proceeds of a spanish property applies only when the sale is by a non-resident of Spain and is, I believe, a payment on account to the spanish government of the capital gains tax due on that sale. Where the actual spanish capital gains tax, when calculated according to the spanish rules is more than 5%, I do not know whether the spanish government expect to recover it from the non-resident.

A charge to Plus valia tax will also have been triggered by the sale, and this is also normally payable by the vendor although it may by agreement be payable by the purchaser. You will know from your contract of sale who is liable.

My expectation, without knowing for sure, would be that the 5% could probably be set against UK GGT liability (HMIT: "Foreign tax credit is deducted from that part of your capital gains tax liability that relates to the gain on which the foreign tax has been paid.")

The 5% may qualify, however I very much doubt that plus valia qualifies as it is a municipal tax.