Can a UK resident legally run a bar/cafe in Spain whilst remaining a UK resident ? TIA

If you reside in Spain you must within 90 days register as a foreign resident, so in answer to your question I would say no

What do you mean by resident?

You would certainly be TAX resident in Spain and so pay income tax on your world-wide income.

Why would you not be resident? If you want to operate a successful business you can't be part-time even with good employees!

I ask because a chap from the UK owns/ runs two bars in the Torrevieja area and has run one of them for several years whilst currently driving a new 2017 car on British plates?

There's nothing to stop someone buying a car and registering in the UK, but that has nothing to do with residence in Spain or income tax.

I suppose it is possible to run any number of bars in Spain and reside somewhere else.

Thanks for your input.