Hi there,
I lived in the UK and now am back in Spain.
As somebody else already pointed out, you will be bound to pay income taxes in Spain... and Taxes here are significantly different to the UK (fiscal year = calendar year). I did have a UK tax advisor and I would strongly suggest to have a Spanish one (by the way, they cost a fraction of the UK ones)
Income Taxes... expect them to be higher. Top rate will vary from region to region but will go from min 52% to 56% in Catalonia (and maybe somewhere else).
Council Taxes... a joke compared to UK ones. Depending on the property you own, but around €1,000 per year.
British Schools. There are a number of good options (Madrid, Barcelona, Malaga, etc.). Tuition fees between 500 and 1000 per child per month. Don't worry about the kids learning Spanish because they will, no matter what school you send them to. Playground language is Spanish!!!
Weather. Well, there is just no comparison... but do expect some cold weather in the winter if you live away from the sea (yes, it does snow in Spain... but we grit and plough our motorways
)
British expats. There are a number of British citizens living by the sea in Spain. I would say mainly Murcia, Alicante and Malaga (the biggest one) but would suggest you blend in...otherwise you will lose a lot of the culture.
Hope it helps
Cheers
fullstep