In the past an E111 was sufficient for Spaniards and I imagine Spanish residents who wanted to visit Britain.  I've been checking out Spanish websites and apparently whilst an E111 still exists, a European Health Card (Tarjeta Sanitaria Europea) is required.  This can be applied for in any Social Security office.  Applicant must show all documentation, ID/Residence card, Cat Salut card etc. Hope this is of some help.

Susanita