I've had plenty of prop weapons and replicas shipped here to me in the UK and never had a single problem.
I agree with obi1al, it mostly comes down to what it's described as on the customs form.
I've had swords, knives, deactivated guns and grenades and even a pair of constantine knuckles shipped here to me, I get them marked as 'Deactivated military collectable/paperweight' for the smaller items or 'Display sword/weapon replica' for the larger ones and have never had anything seized, but they usually get held for a couple of weeks and when they eventually do arrive the packaging will most likely be ripped to shreds and repacked in a delivery bag and the item messed about with a bit :lol
I spoke to customs here in the Uk on the same subject a few weeks ago when I was having some bits and pieces coming in to the country and wanted to make sure it all got here okay, I was told as long as it clearly states its a weapon and is intended for display or a personal collection and clearly looks like a weapon it should be no problem at all.
The only thing they have a problem with and will not entertain releasing is anything thats disguised as something else. Like a sword cane walking stick, or a bond style shoe-knife ..even if it states exactly what it is, they just wont allow it.
Hope that helps a little