Hi Marie
Thanks for coming back to me.
Well at the moment we are in the UK and have a Ltd company.
When we move to Spain in a month, my husband will have to carry on earning to pay our commitments. So he will be commuting to London from Spain on a Monday to Friday basis. If we continue with our company, we fall under the British tax systems.
If, when we move, we close down the company and my husband elects to sub contract to the British companies and commute, we would presumably fall into the Spanish system and pay our taxes etc there.
As our UK house hasn't sold and is being rented for now, we will be looking at the market next year and perhaps getting a sale then.
Under the British system there would be no capital gains as it's our main residence in Britain. In Spain, however, wouldn't it be classed as a second home? I wondered if we would have to pay gains on any profits.
I don't suppose that makes any more sense. 
Laury