"When it arrived it fortunately was just under the UK Customs threshold. Otherwise the courier's paperwork informed me that they would have charged me £50 for clearing it and collecting the fee."
Other couriers have more reasonable policies. DHL for example.
The initial courier charge may end up a fraction higher, but not having to stump up £50 in ridiculous fees makes up the difference.
I'm sure that they can't justify this kind of rent-seeking, but I also suspect that noone can be bothered taking it to small claims to fight it.