I will be travelling from London to Brussels on the Eurostar next week and wondered if our tickets are checked/scanned when we arrive and depart the train? As I have a connecting train to catch shortly after and I know these can take some time when there are lots of people. Thank you for any help you can give!
No, there's no ticket check when leaving the Eurostar at Brussels or any other station. Ticket checks are always performed before boarding.
However it can be slow getting out if the train is busy, just because of the number of people getting off the train with luggage and shuffling down the platform. I recently did a 15 minute interchange (arrive 16:07, depart 16:22) for the onward train to Cologne and only just made it because of that. So it depends on how busy you expect the train to be and what your appetite for risk is.
You can mitigate this a bit by choosing a seat as close to the Brussels end of the train as possible. The seat picker online tells you the direction. You can't choose a seat at booking but you can change it once you have booked up to a few hours before departure.
There are reportedly occasionally spot checks of passports but I have never seen this in the handful of times I've done the journey.
Also 2 useful tips from seat61.com
"Even though the system sells you separate tickets either side of Brussels, you are protected by the Railteam Promise/HOTNAT so if there's a delay and you miss the connection you will be allowed to travel on later onwards trains at no extra charge." From How to buy tickets