Where does Avanti say reservation is required? I see they are sending the "compulsory reservation” attribute to the European Timetable Centre (MERITS) but that doesn't necessarily mean anything. On their own website they explicitly say that reservations are not compulsory (see the FAQ section):

https://www.avantiwestcoast.co.uk/travel-information/onboard/seat-picker

To me that means they are sending incorrect data to MERITS, just like LNER, and the rail planner app and all other timetable planners are then displaying this incorrect data.

This clearly says seat reservations mandatory.

This is on LNERs own site

Again from the LNER site

So LNER are contradicting themselves. On their general page about reservations, they say there are unreserved seats available for people without a reservation:

https://www.lner.co.uk/travel-information/make-a-reservation/

In the FAQ section on that page, they explicitly say that reservations are recommended for pass holders but not necessary.

Reservstions are NOT compulsory on domestic UK trains except for the sleeper services, this is the current situation.

LNER, Avanti and a few others brought in compulsory res during Covid. It has been rescinded since.

LNER management would probably prefer to be compulsory res but it is not the current state, due to the mixed nature of their services with local flows mixed in with IC traffic it is really not a good fit with the way the British network and ticketing works.

Avanti in particular have struggled to run anything close to a normal service for months now, in order to suppress demand they are flagging services as reservation only to prevent bookings however they are not compulsory and anyone with open tickets including interrail are free to board.

I travelled on a LNER a few days ago (with a free reservation) and they announced that coach C was for passengers without reservations and anybody without a reservation should make their way to it. I don’t know whether they enforced it during inspection, but I had to show my reservation.

Reservations are free and available up to 5 minutes before departure from ticket office or online.

Out of interest I far prefer to have a reserved seat wherever possible.

According to the information we have reservations are not needed for most trains in Great Britain the few exceptions are: 

Reservations recommended: Avanti West Coast, Cross Country, Great Western Railway, Trans Pennine Express. 

Reservations mandatory: Caledonian Sleeper, London North Eastern Railway, Night Riviera Sleeper and Eurostar. 

Please do get in touch with us if you're having a different experience so that we can follow up accordingly :) 

So it seems LNER do have mandatory reservations for all trains, but do have one second class coach for unreserved passengers. I would hope that they also release any unreserved seats elsewhere in the train but I would expect on their peak time journeys there will be few, if any, available.

Since reservations are free and available at any ticket office or online from months ahead up to 5 minutes before departure it is surely a no-brainer for pass users to get a reservation, or face the risk of being shovelled into a very busy coach C.

For those not familiar with the UK, LNER operates the East Coast Mainline from London to Edinburgh and beyond, via York, Leeds, Durham and Newcastle.

@Claudi. 

This does not correspond with the GB country page.

In addition, as I already pointed out, LNER explicitly say on their website that reservations are not required. In their FAQs about reservations, they say:

Do pass holders need to reserve seats?

A reservation is highly recommended for pass holders, but not necessary.

So please move LNER to "reservations recommended”. If LNER say to you they have mandatory reservations, then they're just fooling you because that's not what they say to their passengers.

So in short, mandatory reservations are only for Caledonian Sleeper, Night Riviera Sleeper and Eurostar.

I wonder if a comparable situation to LNER’s position is where sleeper trains sometimes have a single coach for seated passengers. To travel in a couchette or cabin you need a reservation but to travel in the seated coach is free of reservation. You obviously can’t move up to unoccupied berths.

Then how do you declare it in a planner? Most seats require mandatory reservations? limited seaats without mandatory reservation? Reservation strongly recommended?  

All LNER trains have seat displays, if it is not marked as reserved then any seat in any coach is free to use without reservations.

I don’t know how many times I have to post this, No day trains in GB require reservations and this includes LNER. Passengers without reservations WILL NOT be turned away or asked to leave the train.

Their management might want to pretend they are an exclusively inter city operation with only long distance passengers who all book months in advance but they still carry a significant amount of people on walk-up tickets and inter-available tickets without reservations.

I now regret asking this question - it was raised simply because there is a wealth of varying guidance on UK train reservations, and I often suggest in answers that visitors can visit the UK and reservations are not mandatory.

Whilst checking IRs own website for a LNER option it clearly stated that reservations were mandatory.

A different search showed a similar situation with Avanti West Coast (see earlier posts).

It is now clear that nobody can give a definitive answer, but my take is now get a reservation for UK trains or risk a long journey standing up. Remember that reservations are free and can be got at very short notice - giving you guaranteed seats together rather than searching the train for seats unreserved for your full journey.

BTW I would do the same for any reservable train in Europe - The over-seat indicators are not dependable and I have seen several instances of them not working or not updated to late reservations from interim stations. (Just ask the passengers on the recent ICE from Frankfurt to Brussels via Cologne - even the indicators with the coach numbers weren’t working, let alone the over seat reservation info.)

On LNER somebody in York can book a seat for the Lon-Edi only 5 mins before the train leaves - bang goes your unreserved seat, at the very least forcing you to go searching again, but probably needing to separate or stand up.