This is more about the how than the do or don’t.
What they’ve introduced is both too broad a ban and with literally zero enforcement measures attached.
So using Spain as the example, the 2 hotspots in Spain are Catalonia and Zaragoza iirc, so ban travel for U.K. citizens to those 2 regions, job done. Anyone already in those regions should face a screening on return and a stringent enforcement of quarantine with tracers contacting their employer and maybe daily contact via phone to the individual with a possible ‘no notice’ visit for a decent percentage of those who should be isolating, with a hefty fine if they’re not at home. This will only be a relatively small number of people so should be easily achievable give the number of tracers they’ve paid for ffs.
The rest of Spain shouldn’t be included. The Costas are showing no current issues nor the canaries or the Balearics, so leave them be.
Just for context here. Spain had 2 corona deaths yesterday, we had 119. But Europe provides the biggest threat or something.