Well, it depends if you have passengers on or not. If a train has broken say in Uckfield, then that would first be taken to Oxted station either being hauled by another train or by loco to allow the passengers to disembark, to catch the service up from East Grinstead. But as option has said above, the train should have backup batteries, so in theory unless there is an issue as well with the backup batteries the train should be able to get itself back to either Oxted station and go into the sidings to await a path back to the depot or if a path is available and the driver believes that with being back on 3rd rail at Oxted that he should be able to get the train back under it's own power to the depot, then he will do so. Otherwise, it will be a case that the train at Uckfield is either rescued by a thunderbird loco or the next service coming down to Uckfield which then drags the train away, again either to Oxted or continues with the broken down train on it's service to London Bridge if doing passenger duties, but once that service is completed then goes off to the depot i.e. in this case Selhurst.
That relies on a rescue loco (and the whole question is whether a non diesel rescue loco can exist) or the units having enough battery power to not only do the trip themself but to also pull another unit.
That doesn’t explain what will have the capability to haul a broken battery unit from Uckfield if diesels aren’t allowed, assuming there is anywhere to get it out the way in the first place without getting it to Oxted
As far as I am aware there is not any sidings within the areas of the stations between Oxted and Uckfield. The only possibility on route, if it they where not being used would be to place it in the platforms used by the Spa Valley Railway at Eridge. But being there would not allow the unit to recharge it's battery. The only choice where a unit would be able to recharge, would be the sidings at Oxted.
There is no physical connection between the Spa Valley and Network Rail tracks.
Or leave it in the platform at Uckfield and Top work then recover it after service ends
Is Uckfield platform 24 cars long?!
Uckfield is 10 cars for a class 171.
This is a speculation thread, and I am speculating that some politician bans diesels and says ‘make do’.
And speculated
If advances in battery tech will solve all problems why do all the traction studies I have read say batteries are not a solution for freight and another solution is needed?
Batteries are not the total solution. In most cases it is electrification that is the answer, with batteries giving power to last delivery point away from the electrification.