Be aware there are major Kings Cross engineering works the weekend after PBP. During this period there will be no trains between Kings Cross / St Pancras / Moorgate and Cambridge or Peterborough (or intermediate stations on the East coast lines) https://eastcoastupgrade.co.uk/the-programme/https://www.nationalrail.co.uk/service_disruptions/currentAndFuture.aspx?TravelDate=24%2F08%2F2019&TOC=gr
That's annoying.
St Pancras also has the Bedford line so trains to Edinburgh will still be running. But Euston, a mile up the road, and west coast likely a better option for Edinburgh.