In reply to mic:
Technically not.
http://www.eurostar.com/uk-en/travel-info/travel-planning/luggage/sports-an...
Dangerous sports equipment
If you’re travelling with any of these items, you’ll need to contact Eurodespatch, our registered luggage service: ice axes and other climbing and mountaineering equipment, javelins, spears and spear guns, crossbows, crossbow bolts, longbows, longbow arrows and starting pistols, swords or starting pistols. Keep in mind that these are all subject to approval and security checks.
There was a period when they were more reasonable but sadly they've gone back to being, at least officially, paranoid beyond belief.