Just as a point of information, when "Ladies Only" accommodation was provided on trains it was usually on the "compartment" stock. Older readers will remember that such stock was divided into small compartments, each one with its own door so that access was only available at stations. There was no access between compartments. The "policing" was thus carried as at the stations as people boarded the train.
This is a particularly fine example of compartment stock which used to operate on the London underground system:
http://www.bluebell-railway.co.uk/bluebell/bash/hist.html
And this is a more recent version which ran on Southern Region commuter services until about 1995 (though not all of this type were compartment stock):
https://en.wikipedia.org/wiki/British_Rail_Class_415#/media/File:4EPB_set_at_Wimbledon.jpg
As far as I know no regular rail service operates compartment stock any longer and almost all conventional stock has access available between carriages.. Even if the idea was deemed desirable the impracticalities of it are probably sufficient to make it a non-starter. However, Mr Corbyn cannot claim the credit for this idea. It already operates in Japan and some other countries:
https://en.wikipedia.org/wiki/Women-only_passenger_car
And Claire Perry, MP, floated the idea for reconsideration here last September:
http://www.citymetric.com/transport/uk-may-get-women-only-train-carriages-344
The facility was scrapped in the UK in the mid 70s I think. To reintroduce it today may need some enabling legislation as it would probably fall foul of gender equality laws. But I think the idea that the only way to keep ladies safe on trains is to provide them with their own carriage is a little misguided. Such facilities would probably prove quite an attraction for those slimeballs who are intent on harassing and assaulting women by quite conveniently arranging for a whole carriage to be the focus of their obnoxious behaviour.