Not a particularly good idea either though, it would be a huge expense and Who's going to pay for it?
Redhill there is probably some spare land after platform 0 is built, but I believe there is going to be Thameslink stabling there.
Gatwick sidings are regularly used already by Thameslink/GWR/Southern.
Salfords is used by freight isn't it?
If any new sidings were to be built then something at Norwood would be far more beneficial, although NR have apparently ruled this out on cost/Benefit
Rather negative response. I said extending Tulse Hill would be expensive and it has been subject to many comments on here about impossibility.
However additional length for trains by providing extra sidings is vital due to the overcrowding all over Southern's network. It's worse for South Eastern but Southern also have a problem of where to put any additional stock. Money comes from providing adequate capacity on cost benefit basis.
I gave examples of potential sites. Redhill platform 0 isn't beneficial as there is no space on that side of the station. There is already a depot/sidings where GWR store 165's in the fork of the Tonbridge lines and there is much Railway owned land there that additional sidings could be put on. Southern already stable stock overnight there on the goods loop and a few extra sidings is not going to cost a fortune but enable the Railway to have more units overall.
Salfords also has much railway land that is not used well but AFAIK there is little spare Railway land at Norwood unless you actually move the main lines.
I am sure there are many other potential examples of Railway land where sidings could be put for additional units around Southern.