edit: on looking again, interparcel have changed the system, so they dont offer as many options as they used to
you should be able to pick up a box free-of-charge from most bike shops. be warned, i bought back a bike from NY recently as luggage (in a bog-standard bike carton) and the front wheel seems to have come out a little buckled, so factor this in when you're packing and who you use for delivery.
edit: on looking again, interparcel have changed the system, so they dont offer as many options as they used to
you should be able to pick up a box free-of-charge from most bike shops. be warned, i bought back a bike from NY recently as luggage (in a bog-standard bike carton) and the front wheel seems to have come out a little buckled, so factor this in when you're packing and who you use for delivery.