Two-part Wedding

Hey folks
I've been planning to propose to my girlfriend for a few months but been put off by the details
She's from Vietnam and has been in the UK for a little over a year on a student visa and living with me for 5 monthsWe want to get married to eventually go for spouse visa then British citizenship so there is a timing element that I'm unsure how to deal withCan we get married quickly at a registrars office (purely for the certificate) then have an unofficial wedding at a venue with friends family catering and all the bells and whistles.Will the big wedding count? Will it have to be officiated? Can we make the 2nd, larger, wedding look like it's our "real" wedding ceremony?Hope that makes sense
Any advice or suggestions will be much appreciated