No, they don't have "siestas". In Spain usually all retail closes from 2pm to 5pm. I wouldn't expect to go to a UK venue and have a normal dining timetables (for me as Spaniard), because I understand things work different there.
mr nacho trying to justify a Spanish tradition. fair enough. but I'm still bold enough to complain about it. it's super annoying when restaurants close from 2 to 5. also I doubt anybody from the foot soldiers actually takes a siesta. it's most likely just basically a variation on unpaid work or being on call unpaid. so, nobody benefits of it except the owners who just optimize the schedule for their purposes.