Yes as MrsJay2be says, I think the difference is a UK/US thing.
Personally though I think you should do whatever works best for you, bearing the venue in mind.
I think that I will go first. I´m getting married outside and have a really long "aisle" walk - probably about 40m, so if my BM goes first then I will pretty much be obscured the whole way.
Plus if she goes behind me then she can sort my train and veil out, which might end up all over the place given that we´ll be outside.