3rd/4th rail at Bedford??
I seem to remember that both trackwork and operating practice only allowed for Mets to cross to H/H platform 1 heading out of town; inbound Mets never used platform 2. (I'm sure I remember that beng the situaiton for many years, anyway.) In fact - did/does 3rd/4th rail even exist on platform 2 (as opposed to platform 1)?
Yes Harrow platform 2 is electrified. Met Line trains can enter the platform from the north, then reverse back towards Amersham via a trailing crossover.
The current rails end at the south end of the platform.
As stated, it has certainly happened that a Met Line train has accepted the signal at the southern end of the platform. Not sure if the train was meant to reverse, or whether it was simply misrouted (perhaps the signalman had it down as a Chiltern train and signalled it from Harrow North through platform 2 and towards Marylebone). Naturally in both possibilities the driver should have queried the route, but sometimes what should happen isn’t always what does happen...
Jumper leads were used to get it back on current, which given the leads aren’t very long would have been quite difficult, presumably having to be repositioned several times. In theory the traction current would have had to be taken off each time the leads were repositioned, and the adjacent line would have had to be blocked whilst all this was going on.