Tha ks everyone for the explanation. Seems far from ideal though, because Three Bridges would be south of St Pancras and therefore not accessible for the 360s. I knew about work being done at Northampton but there's no easy way of getting there - for example, a passenger wanting to travel from Wellingborough (on the MML) to Northampton would have to go via Leicester and Nuneaton, so I assume trains would have to take a similar route (or, as mentioned, going via a London spur). In either case, they can't go via their own traction.
The more concerning thing is, if EMR are keeping the 360s long term (instead of getting more bi-modes like the 80x) then I can't see a way of this situation improving, not whilst major maintenance facilities are not on the MML. I've also not heard of such low reliability figures before - 11 or less out of 21 is not good!
