There is no published literature on this particular case of lexical variation.
Trousers is by far the most popular lexical choice, with over three times the number of responses than pants. It is widespread throughout the whole country, although the strong preference for this lexical choice is weakened somewhat in the North, particularly the North West. It becomes clear that pants is a strictly northern term when one looks at the variation in the North West in particular, where 49% of speakers use pants. In the South of England, this figure drops to a strikingly low 3%.