There was definitely a time when you were allowed to have working lunches in restaurants etc whether this was then, I can't even begin to remember
But this wasn't in a restaurant, it was in an MPs office during a by-election, so "everyone meet back here for a debrief with food at the end of the day" Seems perfectly within those regs if it was in that period
Also the only people invited were party workers, not an interior designer and a few journalists and the bloke that primps the wifes cat. There's also no hint that ABBA was played