Hi mellor7,
The laws of the Supreme Court of the UK preside over the individual laws of England & Wales, Scotland and/or Northern Ireland. I can find no legal reference to "British" laws. UK citizens, whether resident or non-resident in Spain, should satisfy themselves that they understand how they are bequeathing their estate - choosing the cheapest option will not necessarily achieve this. Ultimately, people have to satisfy themselves that they have thoroughly investigated all options and pursued what is best for them.
Kind regards,
Kim