My experience with GWR train from Oxford to London

The online train tickets are sold out

Train tickets don’t sell out.

Trains in the UK do not limit the number of people allowed on to the number of seats, so busy trains will have people standing, and yes it can make for a difficult journey.

There could be a number of reasons why the train you were on was so busy. Other trains could have been cancelled, there could have been crowds travelling to an event or it could just be rush hour.

Regarding people sitting in your booked seats this is not unusual. If they have a flexible ticket people can travel on trains other than the one they are booked on. On a busy train passengers will often sit in a reserved seat on the off chance the booked passenger is not travelling. If the booked passenger does turn up the person sitting in the seat will ‘usually’ give it back. There should be no need to ‘demand’ it back from them.

do you mean October 2025, or do you mean a different month in 2026?

What day of the week were your journeys?

It may be that in your country people are forbidden from the aisles, that's not the case here.

If you had to push through so many people were you late to the train before finding your seat? Usually it is easiest to board the train at a door near your seats, at least in the car where your seats are.

Why did you feel you had to "demand" your seats?

Other than the trains being busy, why do you say it was "Quite Awful"?

How was the rest of your trip?

People will sometimes sit on seats that others have reserved - reason being, reserved seats are quite frequently left unoccupied because the people who reserved them missed the train or decided to sit somewhere else. All you need to do is say "excuse me, we've booked those seats" and they'll move. It's normal practice.

It's pretty common for things to be crowded. It was obviously just a busy day - not sure why it's a problem for people to stand?

In the last 7 days I have had at least 50 seat reservations (I've lost count, but it's used a lot of paper to print the paper reservation coupons!!). I haven't used a single one of them, as I have been on earlier or later trains to the ones I reserved seats on (or changed routes completely), or the trains have had more coaches than planned- so had room to change seats and spread out.
Trains with 11 coaches, not 9- or 6 coaches not 3, that kind of thing.

Yes the trains can be uncomfortably overcrowded at peak times or if there have been cancellations or other problems. People will always take a reserved seat if no other is free. Don’t be surprised by this. Often the reserved passengers don’t travel and then you have the seat. There is basically no limit to the number of people who will be let on to the train.

All things to be aware of if you are not used to it.

We found that when crossing US/Canada Border we were required to be in our assigned reserved seats until customs agents sign us off. On a bus, we all got off and went thru the border office. Have not done this recently, may have changed.