I'm interested to know what the advice is if a train is cancelled, and (such as in the Chippenham example) that train would have been full seating and the next train coming can be expected to also have a full load. Would it be allowed to carry another full load's worth of passengers, all standing?
The standard advise on the ground is still
"listen to the advise of the station staff or help pointer responder who should know the local situation".There's no specific number of people beyond which you're no allowed to join a train; often-given answer here is
"if you feel it's unsafe it's your choice not to travel". There are actually two examples of cancellations from Chippenham that this thread / post addresses.
1. The diversion go the 17:45 to Taunton to run via Westbury, thus cancelling it at Bath, Bristol and other stations on the way
I would suspect that both the 16:30 and 17:00 from Paddington (17:45 and 18:14 at Chippenham) drop off more passengers there than they gain; I'm not denying they 18:14 would have been full / perhaps so full it couldn't cope, but it would have been somewhat less of an issue than putting "two into one" might suggest.
2. The cancellation of the 17:53 to Westbury.
Suggestion for Trowbridge and Westbury passengers - catch the next train to Bath and change there; you'll be into Trowbridge at 18:53 and Westbury at 19:01 - that's 40 minutes after plan, but better than waiting for the next train which doesn't leave Chippenham until 19:05. "Via Melksham" tickets are honoured on this route in the event of such a cancellation, but let the station staff at Chippenham confirm that. The 18:36 bus from the Chippenham Station forecourt doesn't arrive in Trowbridge until 19:23.
Passengers for Melksham ... the 18:36 bus arrives Melksham Market Place 19:03, and the following train at 19:05 reaches Melksham at 19:15. Even with the bus, that's an hour's delay and marginal for what the station staff choose to do. Nothing to stop you forming your own "groupsave" club and 4 of you sharing a taxi at your cost if
GWR▸ don't.
Interestingly, if Melksham passengers arrive at Chippenham before 17:45 to find the 17:53 cancelled, their quickest route is to catch the 17:45, change at Bath (18:00 to 18:07) and Trowbridge (18:29 to 18:38) and get to Melksham at 18:47 - just 44 minutes late. That presupposes that everything else is running to time, and the problem's not due to a train failure (as the 18:38 from Trowbridge is formed of the same unit as the cancelled one). Ticketing also potentially an issue on that one.
Although the 17:53 off Chippenham is usually full and standing (and more standing!), by the time some traffic heads off via Bath and others wait for the next train at 19:05, that train won't be packed or anything like. Apart from anything else, the 19:05 is twice as long ...