They are actually running almost as comprehensive a train service as the available infrastructure allows but with what may appear poor decisions about exactly what is being run - the issue is Network Rail taking possessions at three locations and GTR's thought that people will be put off travelling by buses being involved.
Possessions are:
All lines Gatwick to Three Bridges (exclusive of stations) to do work at Tinsley Green Junction
Slow lines Purley to Windmill Bridge Junction and Norwood Junction - East Grinstead line closed
All lines Norwood Junction to South Bermondsey Junction
There is 11tph through 3 platforms at East Croydon - 5tph from London Victoria to Gatwick Airport - 2 x Gatwick Express non stop, 2 x Gatwick via Quarry, 1 x Gatwick via Redhill and, taking up the most capacity, 2 x Caterham stopping on the fast line from Balham to Purley - the other 4tph are 2 x Thameslinks and 2 x London Bridge to Tattenham Corner.
The Caterham service means that the Victoria to Gatwick services need to be flighted - the Purley Oaks and South Croydon stops are in the Tattenham Corner train. Only 1tph via Redhill to accommodate the GWR service from Redhill to Gatwick (ie platform capacity at Gatwick with platform 2 closed)
The problem seems to be that demand is now such that this kind of cut back in service can't cope with the demand on the Brighton line and they need to come up with a way to run more / be a bit more inventive.
