Just got back from London today and I was very lucky indeed, as I decided to pop into Euston on speculation to see what the options are and it turned out there is an Avanti train to Liverpool and LNWR cross ticketing is allowed leaving within 10 minutes, needless to say I jumped on it, there was only about 25 passengers on the concourse waiting for a train with most going to either Northampton, Manchester or Liverpool, I'm glad I popped in as I didn't relish the prospect of 7 hours on a Megabus fronm London to Liverpool.
The interesting thing about my journey is it didn't go over Runcorn bridge, instead it went by a different route via Earlstown junction and 3 stops Stafford, Crewe and Liverpool, very lucky timing, however there is no local trains running in Liverpool so I got the bus home.
I now have an non refundable unused £11 megabus ticket which I'm happy to lose as long as I got home actually earlier than my original return journey would have been.