Reservations in the UK are free and optional. Don’t use ACPRail which will charge you!

The pass is your ticket. Log the train on Rail Planner app before boarding and that’s it.

If you wish to make a reservation (recommended on London - Manchester) use GWR or another operator. See : https://www.seat61.com/interrail-and-eurail-reservations.htm#UK and

then is this a lie?

Seat reservations required

You need to buy a seat reservation to board.

Not available from Eurail.com

This seat reservation can’t be booked on our website. Check 'More information' for other ways to book.

It is a known issue that some British trains are listed as reservation compulsory when they are not.

To be clear, all domestic trains in GB are available to be used without reservations with any valid ticket. The only exceptions are sleeper services and Eurostar traind to France/Belgium/Netherlands.

Eurail is valid on all railway companies in GB except Heathrow Express, London Underground and metros/trams in other cities.

Reservastions are optional and available on some routes and can be obtained for free from ticket offices or online, paying ACP for them is just a waste of money.

The links @thibcabe provided are comprehensive, accurate and up to date.

It’s a mistake in the data. Reservations aren’t required.