The 16:00 BRI» never got dispatched and was cancelled. It was then turned into the 16:30 and then every commuter under the sun decided to get on that one train. TM▸ Refused to take it on safety grounds.
Not to call order issued for RDG▸ (but it did stop there).
All platforms all over the place, trains all over the place.
The 16:00 now 16:30 left at around 17:10.
Loads of westbury people tried to get on assuming that because every other day of the week it goes from platform 8, it would today. READ THE SCREENS this is a Bristol train, no its not the westbury train.
When I arrived at Paddington at about 16:55 I saw that train in Platform 8 thinking it might be the 17:06 but I did read the screens!

Yes it was very full but I've seen worse, I don't know exactly why the TM refused to take it? However by that time the 17:00 to BRI was on the screens so maybe people had transferred to it. (indeed if my memory serves me right it actually left before the 16:30!)
One other example of the chaos - the 17:15 to Swansea departed from Platform 10 and went on the relief line to Acton where my 17:06 overtook it on the main. (and then no doubt the 17:15 was further delayed whilst the 17:06 called at Twyford!)