My usual avenues would be
1 Check FreeBMD for the entry - sometimes (especially if its one on my tree) there may be an envelope icon which is a postem and has the details transcribed
2 Put the GRO ref (Year, quarter, vol, page) into Marriage locator
https://one-name.org/marriage-locator/to see if you can determine the venue.
Sadly this one comes back with a result of Register Office, so parish registers/ Free Reg/Family Search etc are not going to help and cert is the only option.
3 I'd also look to see IF there was some sort of announcement in the newspapers which may help
3 check online trees on the offchance someone may have more detail and is willing to share
4 If that all fails and the budget permits, order the cert
Boo