Can you buy duty free on eurostar to Brussels?

No. There is no duty free travelling between EU countries, no matter what means of transport you use (air, train or by road).

Eurostar is the brand name of the company running high speed trains London-Paris and London-Lille-Brussels through the Channel Tunnel.

Eurostar uses the stations: St. Pancras (London), Gare du Nord (Paris), Bruxelles Midi (Brussels) and Lille Europe.

Currently these are the only passenger trains operating through the tunnel.

The Eurostar takes 2 hours 15 minutes between London and Paris.