We are so unhelpful at times. Apologies. Without knowing anything about your event, setting, etc., I know that COSTCO, which I believe is in the UK, has a bakery and also does some catering options. I would check them out. If you have people who can pick up, set-up, etc., it could be what you are looking for.
I had a graduation party several years back and did most of my shopping at CostCo. It turned out really nice. Nope, it was not going to be a sitdown fare, but it was a nice buffet and no one realized that it came from COSTCO.
Just my two cents.
Edit: If your COSTCO can sell alcohol (mind does not,) the wine, beer, and other selections can also be quite reasonable. I have a friend who is into wine, and was surprised that we could find "acceptable" choices. As for me, I'm the reason that "Two-Buck Chuck" sold.