I also keep a van in spain under british insurance and taxed and mot'd in Uk. If you take a vehicle over on !st Jiuly you can keep it there for six months of that calendar year, plus six months of the following year so it has to return to the UK in time for a new mot. As I have more than one vehicle I simply swop them over each summer keeping one in Spain and one in Uk. My Insurance allows me to drive anywhere in Europe for up mto six months per period of insurance so that is renewed 1st jan each year. I am travelling back and forth each month so this is a legal and sensible solution for me.
Steve