Jack.

      I know it makes no difference to these UK cowboys with no insurance but from Oct 2014 you do not have to display a tax disc on a UK registered vehicle. (You still have to pay the tax)

https://www.gov.uk/government/news/vehicle-tax-changes

    The only good thing is all UK vehicles in Spain after 6 months now must be put on Spanish plates.(Unless on holiday) They may get away with the " I am on holiday" Lie once, Never mind the cement stained clothes but your vehicle Reg will be noted and the next time It's  :'( :'( :'( :'( :'( 

I bet none of them have complied with these DVLA rules either I know some have been here for years.

https://www.gov.uk/taking-vehicles-out-of-uk