@rubenwardy its not just Eurostar - people are like it at the airport too. As soon as they've got the thing they need out of the tray, the tray disappears from their consciousness and they think you're being unreasonable for expecting them to clean up after themselves.

I've found it best to just think in terms of "cleaning up before" being the etiquette, for my own mental health 🙃 same at the gym with weights.