Hrm. It seems to be classed as a 'normal' day by Royal Mail, yeah, but not by any of our couriers (APC, DPD, FedEx or UPS)... Maybe PF will fall under RM? Hope they do for your sakes!
Edit: Had a further search and can't really find anything conclusive... All the specific dates seem to be posted on the RM site, however it does include info about PF pre-Christmas, so hopefully 31st will be a normal day for PF! http://www2.royalmail.com/greetings