Its like this:
There is a line block from Stevenage to Biggleswade on both up lines.
Up trains are doing a double shunt to access the down fast, and thats being worked under SLW to allow moves in the up direction. Adding complication is the fact that trains are coasting under Hitchin OHNS in the up direction (obviously for those not paying attention, this is still on the down fast). Obviously, its one train in section on the DF from BIW to SVG.
The story about a broken down train is actually incorrect, there seems to be a problem with 365's doing both SLW and COASTING, causing a problem with the AWS, but thats where it all started. An FCC train was stuck in the coasting/SLW section for about an hour. With a back up of 6 trains by the end of that incident, including another two FCC. The second FCC went through and had the same fault as the first , job stopped for another hour whilst it tried to go back so by this point its just a mess.
When you consider that there is a double shunt, and then a hell of a long section to be gone through its just meant that everything for both FCC and EC has been totally out of kilter, stock and crew.
The service for both is still on its knees, and I doubt it will be fully back to normal till tomorrow.