Ive often thought about taking a spin on a diversion over the years when I’ve had a decent PNB at Liverpool St but have always bottled out incase something goes wrong.
That makes me laugh. That's the sort of thing I would have tried in my time on the job, only to find that on the day I chose to do it, the S.H.ONE.T would hit the fan....
If Liverpool St has been closed, has this ever taken up trains to eg Norwich and Ipswich?
No, as others have said. It's not only about pathways or platform availability (at Fen St), but also about safety. With so few potential paths and plats available, as soon as a through service (to London) is advertised, the world and his wife who would normally travel to Liv St, from Norwich inwards, will try to board what would be a very limited service to Fen St and cause mass overcrowding and potentially a very dangerous pubic order situation. Hence such things in all TOC areas, will be avoided, where there isn't sufficient capacity.
I've had personal experience of trying to deal with crowd control issues at certain stations, when the location was completely overwhelmed, and it can be bloody frightening for those on duty, and potentially very dangerous for members of the public, who seldom understand the risks involved.