The problem affecting the standard definition services which normally run on channel 103 on BSkyB. ITV services on high definition (HD) on Sky channel 178 appear to be working normally . FreeSat is affected too - Freeview services are working normally.
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The RMT Union's comments come as it's announced a new operator will takeover the South West Trains franchise.
Monday's forecast for the west of the region
Monday's forecast for the east of the region