Lumina - I put through a MASSIVE BPTP order, and 1 box got grabbed by Customs. It contained 7 L'Autunno sets and 1 Inverno set (to give you an idea). The customs charge was £10.81 (plus the Parcelforce 'handling fee' of £8).
This is the 2nd group order I've done myself and the 10th or so that I've been part of. Customs gets tons of parcels, so the odds are high on yours zooming through!
Hope that helps!