Mark, VAT is more like a sales tax. It's levied on most goods and services in the UK (and EU as a whole) so anything you buy over here will include an element of VAT in the price. UK VAT rate is 20% at the moment, although certain categories of goods are exempt (food for instance).
So if something is bought from somewhere where the goods were not originally subject to VAT, an assessment of the value of the goods is made and VAT levied at the prevailing rate. Items under 15 value aren't subject.

This also goes for services such as camera repairs - so if I sent a Hasselblad off to Mr Odess, for instance, I could expect to pay another 25% on top of his bill when my camera arrived back.

It can be a bit of a lottery. I've had plenty of stuff over 15 (but way under 100) come through OK from all over the world. So one could get lucky even with a costly item, but the potential extra cost has to be allowed for.

pgomena - Perhaps it's about the volume of cameras available? Presumably 35mm cameras sold in much much larger volumes than MF cameras.