'trolleys' or 'trollies'

[dublintuition]

Which?

I would have said 'trolleys', but I'm looking at a book now, published by folens, and on the higher level LC course, which says 'trollies'.

Checked the Oxford Advanced Learner's dictionary, and that quotes 'trolleys'
so whats the deal with 'trollies'?

I'm fairly sure that because the last letter before the 'y' is a vowel, that we just add 's' and not the typical 'ies' after knocking off the 'y'