From the FGW▸ website :
16:30 Cardiff Central to Portsmouth Harbour due 19:54
This train will run short formed with 3 carriages between Bristol Temple Meads and Portsmouth Harbour.This is due to a train fault.
Bit premature with that announcement as we picked up a 150 at
BTM▸ , although we were late away due to a few technical hiccups, and we were delayed further due to following the
HST▸ .

I'm assuming that the 1722 off BTM is now booked 5 car considering the official announcement, I think pretty much all seats were taken last night and I can see it becoming a service of choice if there is a guaranteed seat. Interesting it doesn't stop at Bradford, would be nice if there was a 42 min journey the other way in the mornings.
