UPDATE:
Cancellations to services between London Paddington and Reading
Due to a fault with the signalling system at Twyford fewer trains are able to run. Disruption is expected until 23:59 21/04.
Train services between London Paddington and Reading may be cancelled, delayed or revised.
Customer Advice
We apologise for the disruption to your journey today.
Due to a significant signalling fault in the Twyford area, trains are unable to operate on the Great Western Mainline.
Trains will be moved to stations where possible and hold there pending a fix to the signalling. Network Rail teams are on site at Thames Valley Signalling Centre and at Reading, working to resolve the issue.
This is affecting train services from Reading to Basingstoke, the West Country via Newbury Westbury and Taunton, South Wales, Cheltenham Spa and Oxford and the North Cotswolds.
Sounds like a major outage this afternoon. Nothing is leaving Paddington High Level other than the Heathrow Express
It doesn't have to be a major outage to stop all departures. The stranded train policy is brought in. Wherever possible trains are stopped in platforms and don't move until the problem is resolved. This is to prevent passengers self evacuating onto open railway lines.
There was a rule book alteration many years ago, a new reason for a driver to be authorised to pass a signal at danger, proceed into a platform where another train is stopped, think for example Keysham or Nailsea.
Today's 1530
BTM▸ Paddington had a delight 2 hours at Chips and Ham, 1530 Paddington WSM is currently 222 mins late!