Its free on LNER trains too. Until recently you got a code when you booked tickets on the LNER website. But now its free for everyone no matter where they bought their ticket ( no code needed).
The WiFi should be free anyway, especially when you're paying over the odds for a train ticket.
@cb-uk is right. This has been my experience for the last few journeys I have been on with them. You can get a free WiFi code through the Virgin Red app anyway.
I get offered free WiFi through the virgin red app.....it has NEVER worked! Signal sucks, they have a cheek charging for this.