Is it also possible that (not necessarily supermarket workers) but other non essential shops, offices etc. furloughed staff for months on end. Those workers still accrued their holidays which means that as well as their annual leave they are entitled to the holidays they would normally have had if they hadn't been furloughed. I know this has happened in our office - the workers who were furloughed (not me unfortunately) have loads of annual leave to catch up on meaning that everyone else has to cover.