Recognition of Gambian marriage certificate

[recro]

I have been married to a Gambian national for three years and she would like to visit me in Spain. I'm a British national and long term permanent resident in Spain. In order to have our fully legalised Gambian marriage certificate recognised by the Spanish embassy in Dakar, we need some declaration that it is legally recognised by the British government/legal system.
Without this, no visa. The British Embassy in Gambia or Senegal no longer do this. Anyone have any idea how to proceed??