There is also a differance between a wild species expanding its range into britain and an escaped species naturalising in britain. Collard Dove was a species that expanded so was already on the british list before it became very common, whilst other species escaped and then formed breeding colonies ie Ruddy Duck, and once these were self sustaining they were then added to the list. Also do native species have to be breeding species. I would class pink footed goose as native as they are very common up here in norfolk in the winter, and are swifts native as they only spend about four months here a year when they breed.
I think part of it is down to personal intepretation, its all very confusing!!!!
