UK Citizen married to Indian national

[ex_brit_girl]

Hi,
So we have found out that our existing marriage certificate (which was issued in India) cannot be legalised in Spain. They can only legalise a document that was issued in the same country.
How do we get them to accept our marriage certificate.
NB) In order for my husband to get his residency permit in Spain, they asked for a Spanish translation of our marriage certificate. This was acceptable for him to live there so why won't the British govt accept it?