Spain is now one of many countries that use VFS for their visa applications see http://es.vfsglobal.co.uk/
Yes, as the spouse of a British national, the visa fee is free but as they now use VFS, VFS charge a fee of £24 per application.
I went last year to apply for a visa for Chuchin for Sweden at the same office, even though you have to book an appoinment, when we got there we had to take a ticket and wait for over 1 hour
Good luck and hope you enjoy your trip
