Around 1000hrs a rough ride / rail defect was reported and it appears most if not all traffic had to be stopped to allow an investigation. All lines are now open but there is a speed restriction on the Down Slow. It took some time for the speed restriction boards to be put in place and therefore, until that happened and to avoid unnecessary delays whilst drivers communicated with the signaller, some services avoided the problem using the Down Fast instead. Unfortunately that caused congestion, with delays very quickly building from 1030 onwards. Actual loss of time through the affected area is now minimal, but the main issue now is that service recovery has not been terribly quick. With today's warm weather it looks like Network Rail's heat contingency measures are in place, meaning some junctions cannot be used to their maximum extent of flexibility, so trains can't necessarily get back in the right order by overtaking each other on Fast/Slow lines, etc.