The legal bit of your wedding in the Registry Office will not just be form signing. You will have to go through the whole wedding process. The whole "I do" bit.
You will need to prove who you are, so passports.
You will also need your Decree Absolutes.
Notice has to be served prior to the Registry Office wedding, I believe three weeks is correct.
And you can't just turn up. They will tell you when you can do it, it takes about half an hour.
And since this is the busiest time of the year, you could be in for a long wait.
And it might not necessarily be your nearest registry office either. Depending on where you live you might actually have to visit another one.
It is not that easy to "just do it" I am afraid, it takes some serious paperwork and preparation.
And checking of documents. They have to be very careful that people marrying are who they say are and are doing it for the right reasons.