Great Western Coffee Shop

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Only guessing but it may have something to do with infrastructure capacity. May not be possible to have all services operating so only operate certain services and I suppose its easier to have just 1 TOC opeating a more frequent service as opposed to 2 on a verymuch reduced service. Again though I am only guessing

With snow part of the problem is that points can get blocked with snow.  When there is a lot of snow around there is a contingency plan to keep certain points in one position only.  Then only some services will run.  I should imagine the points at Redhill are set to allow trains to run from London through to Gatwick so FGW have to terminate at Redhill.

You can imagine the problems if the points froze after being set to allow the one FGW service an hour to go to Gatwick. Then all trains from Victoria to Gatwick brighton etc would be stuck. 

The same thing happens on the Marlow to Maidenhead run.  When things are particularly bad through trains to London do not run.

It's called the "Key Route Stategy" and all companies / NR routes have them.

Yesterday, I travelled on the North Downs line and then on to Croydon and back to Reading via Staines.

The snow in East Surrey was and is pretty deep and, at Redhill, a route had been cleared through the platform lines - the through lines were not visible and presumably the Quarry line was shut - all trains (including those not stopping at Redhill) were passing through platforms 2 and 3 with Reading trains terminating in platform 1.

Therefore, no points were being operated on the through lines at Redhill (with only the point operational being that to let Reading trains in and out of platform 1).

Having Reading trains operate to Gatwick would require quite a number of extra sets of points to be operational at Redhill and Gatwick.