Can I keep my UK car insurance for a year in Spain?

This may be a dumb question, but do I keep my UK car insurance whilst living in Spain for a year, or change to Spanish??

Not many UK companies allow you to have more than 3 months out of the UK. Some do, like Saga, but you have to contact them first.
Again, unless you pay extra, UK insurance companies will reduce your cover to the minimum required (3rd party only). Also remember that breakdown insurance is compulsory in Spain and is included in Spanish policies but not in UK ones.
If you are a UK resident, you cannot use a car in Spain for more than 6 months.
If you are a Spanish resident, you cannot keep a car on UK plates for more than 6 months.

You don't say if it is a UK registered car but, if it is, the UK MOT, road tax and insurance must be valid for the entire stay. You can't MOT a UK car in Spain although you can update the road tax on line (provided you already have an in date MOT).
There is nothing to stop you using a UK insurance company but bear in mind the restrictions.

Ok, thanks, so we can keep our UK insurance to get us there, then change to Spanish? Any recommendations please? What happens when our mot is due then? By then we will have had to change registration to Spanish.

To change your registration to Spanish, you have to put the car through the equivalent of the MOT called an ITV. This is valid for 2 years in Spain.
To register your car on Spanish plates will cost about €1000. You need to change your headlights to European ones and your reversing light, if only one fitted, to the other side of the car.
There are many people here who keep their cars for a lot longer than these periods. I could never advocate doing that but it seems a bit of a hassle to bring a car over just for a year and go through all that rigmarole.
Of course, for an EU citizen going to UK it would be exactly the same so it isn't just the Spanish being red tape mad but they do tend to charge rather a lot of money here compared to UK.

Thanks for your help.
Maybe we'll sell the car when we get here and buy a Spanish one

Diane it seems to be as long as you don,t get caught ie have an accident or pulled by police there,s loads of brits running round with illegal cars licence,s illegal mot,s your licence is only valid with uk address it,s a minefield and to some people pleading ignorance is bliss,but our Spanish police carry guns,personally i,d rather be legal my uk car cost me 650€ to swap to Spainish inc a lovely solicitor who even took me to itv station,don,t know what car you have but mine was megane scenic my headlights were bought on ebay 40£ just a thought,if you change before 3 months i don,t think you pay import duty,from memory it was 120 solicitor 70 change documents to spanish 100€ first itv,about 150 emission thingy suma ? For year and one or two other little bits, 1800 diesel by the way

NFU insurance cover has no time restrictions on it when taking or using your car abroad. We always use them and find their rates competitive. You also get to speak to a human!