problem with EuroStar (train through Channel Tunnel) is there is no checked luggage type options so ALL bags are checked via Xray scanners and body has to go through metal detector and then probably patdown.
I've not traveled Europe at all. All I have to compare it to is airport like security. The Eurostar, whatever that is, being more like an airport-like security just got me thinking he might be able to check it if not carry it. But I fully bow to your expertise.
If you don't go through metal detectors just wear it maybe.