rallycinq is right.. if u force it the blade will catch and ital end up flipping out and cutting the surface and ruining ur finish.
just be patient and take it slow.
oh btw, in my experience, Only the b&Q warehouses well rotary cutters... the normal B&Qs dont seem to stock them around where i live. My 2 b&Q warehouses stock 2 types, the dremel one and a less known branded one. i have the less known branded one (it was cheaper and came with more blades etc) and it does the job fine, and the better quality dremel blades are interchangable too
do you mean holesaws - that have a drill bit in the middle for a guide and they attach to a drill?
i'd use something like that if it were me.. but slowly so you dont heat the area up and bugger the paint with the heat (seen it happen on other painted metal surfaces)