I'm just having a poke around trying to plan a journey and using one of the above would seem to be the best value way of making the journey I'm planning but I note that since LNER did away with returns on this route they've also added a via Peterborough restriction. Usually this wouldn't be a massive issue as I'm sure the overwhelming majority of passengers would be happy using an LNER service rather than something more exotic like EMR via the MML. But with there being no LNER service from London or Peterborough I'm wondering if any extra validity has been granted for that weekend to allow passengers to travel on EMR via Sheffield instead? If not then it doesn't appear that there's any easy way of doing this journey on a flexible ticket!