You could also try Mollá, Rudiez y Oliva. They are basically 'gestores' and economists (they have at least one lawyer on their staff), and seem knowledgeable on tax issues, both Spanish and UK.

I haven't used them myself, but they (Flix branch) successfully resolved a complicated problem for some clients of mine. Some of their staff speak English.

They have various offices throughout the province, including Mora d'Ebre. If you google search their name you will find their website.

Hope this helps

AgentX