Which Route? Edinburgh - London Euston (West Coast Line) or Edinburgh - London Kingscross (East Coast Line)? both are operated by different railcompanies West Coast by Avanti & East Coast Line by “LNER” London North Eastern Railway :)

You can search on Facebook their pages and write them a message with a reservation request (for me it was back in 2019 free and quite easy but please note that they reserve just 60days in advance and you are to early for June )

Hello , thank you for the information ! It’s from  Edinburgh to London kings cross 

The usual route is via east-coast and THIS company=LNER is-as for now-listed as needing to REServe seats with a pass. There is ALSO now a low-budget competition on this line, named LuMO-it does NOT take passes.

Its simply way too early to book for june now. In fact: there are hourly trains with each some 500+ seats, so a day or 2 in advance, when you are in the UK already anyway is really sufficient. Then its free at any counter.

And the avanti trains via west-coast are without need to REServe, so there is always an alternative, be it a little longer to take.