As a friend I would rather see the ceremony. Can you do that, followed by a festive DIY appetizer buffet with champagne, and then those who want can follow along out to dinner?
What distances from home/registry office/pub etc. are we talking?
The invitation could read:
Join us for wedding of blahblah blah at 2pm on xx date
Champagne reception and hors d'oeuvre 3-5pm at the home of xxxx
All welcome to join the bride and groom at the Fox & Lamb from 6pm - ?
(view menu at xxxx.com ~ separate checks)
I'd keep a spare hundred quid or a credit card handy in case any particular guest misunderstands and you have to pick up their tab discreetly at the pub, but most people should get the drift, or it can be made clear via word of mouth at the afternoon reception.
For the reception, cheeseboard, crisps and dips, pigs in blankets, crudite, olives/pickles, nuts, maybe a warm brie if you have the capacity, plus champagne, beer, Coke, tea would be plenty. And a nice little cake.
If you don't want to do the pigs, a cold sliced ham and some good bread or rolls or croissant is elegant and goes well with champagne or beer. You don't have to serve a million things, in fact simpler is more elegant. Anyone should be able to make do with a small ham sandwich, a few slices of cheese, the odds and ends. It's just a snack. (btw ham and havarti cheese on a croissant is a taste sensation and I can vouch goes well with fizz!)
If even that is out of the budget, there is nothing wrong with just the wine, beer, a cheeseboard and some nuts. Your family should be able to help with that. Get more champagne than you think you'll need.