I have took advantage of the east coast offer £10 anywhere and purchased a ticket from kings cross to Edinburgh. Will this be valid to Haymarket or only Wayverley, I thought I had put Haymarket in the destination but my ticket just says Edinburgh, many thanks in advance.
I might be wrong here but, I don't think it's valid.
There isn't an Edinburgh stations ticketing group, tickets are printed with either Haymarket or Edinburgh. Unlike tickets to Glasgow, which are printed Glasgow Cen/QST and are valid at either station.
However, in my experience the barriers at Waverly accept tickets to Haymarket and barriers at Haymarket accept tickets to Edinburgh. The barriers also swallow these tickets, which they really shouldn't as the passenger might only be breaking their journey at Haymarket before travelling onto Waverly later, however unlikely it might be. (if travelling from the North/West)