Just out of curiosity, is there a list of DOO worked lines on Network Rail infrastructure? I'm sure the forum could cobble one together if one doesn't already exist.
In theory every single piece of Network Rail could be used in DOO mode. 99.9% of freight traffic is DOO. The only freight trains that still have Guards (as far as I am aware) are the Nuclear fuel traffic. Every other freight train operates in DOO mode.
Virtually 70% of passenger services is DOO in the London area (the former Thames Trains is 100%, Chiltern Railways was until the introduction of Class 67 operation 100% not sure now, London Overground is around 60%, First Capital Connect is 100%, Greater Anglia is around 80% with all suburban and some longer distance services operating in DOO, C2C is nearly at 100% with only 12 car operation excluded from DOO, South Eastern all suburban and some main line including HS1 services, Southern all suburban and some main line, South West Trains 0%). Ironically Waterloo is the very last main line station in London where all Passenger services are worked with a Guard. All the others having some form of DOO operation.
The introduction of New trains where Drivers open doors, is a form of DOO through the back door. London Overground would therefore be around 95% DOO in one form or another (with only the Gospel Oak to Barking and the one pixie buster from Woodgrange Park to Willesden Junction being the only services operated in conventional mode) and the same could be said for those companies that use the Electrostar fleet ie Southern and South Eastern, So it could well be argued that the figure of DOO operation and partial DOO operation would rise into the high 90% of services.
I cannot speak for services outside London, but I am sure the form of driver opens doors and Guard closes occur on the pendoleno stock and the voyager stock (someone who works on these trains can clarify if this true). That would push the DOO figure higher.
Notwithstanding the proposal to make the GWML completely DOO when electrification is complete.