This puts what I said above in context.

After we married in RoP my wife and I came to Spain 8 years ago. In order to get my dependent’s allowance on my OAP I had to send an original copy Marriage Certificate, or an authenticated copy, to DWP. I could not find an original so I took a copy to the Town Hall, they copied (the copy) and certified their copy as a ‘true copy of the original’ which they believed it was.
I sent the town hall copy, certified to DWP and received the allowance.
It was a few years after that, that Spain stopped the practice of town halls, solicitors etc providing copies.