Whilst there are hundreds, if not thousands, of Brit expats working in Spain, they are generally in the lower paid service industries like waiting on tables, glass collection, cleaning etc. There are reception jobs (our solicitors has an English lady working there and our car dealers has an English lady in the service section) but you would need to speak fluent Spanish for those types of jobs.
Some estate agents employ Brits to work for them to show their Brit customers around but, again, fluent Spanish would be required and most of the ones I've spoken to speak several languages.
Don't get your hopes up too much. Spain is not the cheap place it used to be and you would need to be earning an absolute minimum of 600 euro each per month to become a resident plus you will need private health insurance which could cost around 200 euro a month before you get a proper, pukka gen job with a contract that will cover you for healthcare.
Many of the workers in cleaning jobs and so on don't have proper, contract providing jobs so have to continue paying private health insurance to keep them going.
As said, quite a lot of done it. Most of them work for Brit concerns like cleaning companies, hairdressers, bars and restaurants etc. Working for a Spanish company and we come back to the fluent Spanish bit.
Best of luck. It is worth it if you can manage to do it.