So is it imported by immigrants or not?
Also I love the fact that you bring in "the Catholics" but not "the Protestants". Worth noting that in celebrating all things 'English', England stayed Catholic (both officially and unofficially) for much longer than a lot of other countries.
Pretty sure that St David's day and St. Andrew's day aren't holidays in Scotland and Wales. St Patricks day is in Ireland, but thats because it is a religious feast in a very observant country. If England needs a national day, why make it St George's, when so few people in England are practicing...