Indeed, the Jubilee has George McInulty as a reliability director......is this another case of jobs being created for the sake of being created??? Maybe a different thread.
As someone who works on the Jubilee, it is a lot more reliable nowadays. Sure, we still have failures here and there, but they are getting less and less. I am convinced however that during the Olympics, there will be a high profile train breakdown/tunnel evac at some point. Maybe I am being negative. Like I said the Jubilee breaks here and there, but boy are they proper failures!! Such a busy line and a bit of delay and troubl soon flares up quickly.
As for the other lines, yep the Circle I would say, so much at the mercy of other lines whose track it shares. The Vic can be awkward, usually infrastructure failures around Brixton.
The Northern has improved immeasurably in recent years. Signal failures and faulty trains are much rarer these days.