Google maps statelite and google maps 3D does show the Brook House Farm track to be open. So there would be good vision.
The advantage of cycling this route is it is the shortest route.
It is all good to perfect terrain. Head, Church and Maldon road is tarmac roads. The Brook House Farm and Pages Lane tracks are suitable for cars, let alone bikes.
Bamber knew the route as he drove it every day.
He would want to spend as little time as possible travelling. Could cycle it in 12 minutes at 80%+.