The Victoria Line is currently part suspended "due to while we fix a track fault at Victoria". The suspension is Victoria-Brixton southbound but Brixton-Green Park northbound.
Does this mean the trains are using a (presumably trailing) crossover north of Victoria that can't be used in passenger service? What sort of service level are they managing to run with that set-up?
Presumably the fault must be between the reversing siding and the platforms at Victoria for them not to be reversing there?
They must indeed be using the trailing crossover north of Victoria, but this crossover certainly can be used in passenger service.
I believe it is likely to be more a question of logistics. Having just the one platform for arrivals and departures at the busy Victoria station would be an absolute horror show. Best to terminate at Victoria southbound, get people off the train service and then head back empty, re-entering service at Green Park.