I was on the 1945 Leeds to Kings Cross. Things did not get off to a good start because it was soon announced as we left Leeds that there was neither a trolley in standard and the buffet counter was closed "due to staff shortage", but the train manager put some crisps and bottles of water in boxes on the floor in the buffet for passengers (standard included) to help themselves, but this in hindsight might have been a mistake because all the water on the train seemed to have gone then.
We ground to a halt north of Peterborough and stayed there. For 2 hours. Though some other trains did pass (at least one HST and an EMT 158). The guard made a couple of announcements that it was a broken down train in front of us. After about 2 hours the guard told us that the plan would be to reverse back to Grantham where either taxis would be arranged, or a diesel train would be waiting.
It took a while to get going again and once we did he advised that the plan had changed and that now there would a diesel train in another platform at Grantham. This would head north to Newark and then divert on another route to London (not sure which), avoiding the broken down train (which was of course OHLE damage). He advised passengers to gather all the belongings up so we could make a quick transfer. I was getting really thirsty now but the free water had gone and the buffet closed. By this time the toilets were in a foul state too (the one I ended up having to use had a lot of blood in it, which was a little worrying).
Once we arrived at Grantham there was initially no staff, but at least the waiting room was open (though only room for those that got off first) and no "resuce" train. An announcement was then made that the resuce train was "15 to 20 minutes away" and when it arrived it would be waiting another 2 trains to arrive before it would depart and that it would only go as far as Peterborough, where we'd have to change (again) to an electric service. Suffice to say, this did not go down well with anyone and there was a fair bit of shouting. I guess they'd realised there was no chance of finding enough taxis in somewhere like Grantham at that time of night (and perhaps a realisation of the cost, too).
I did observe some of the passengers helping themselves to the bottles of wine and plastic glasses left unattended in the galley area of 1st class when our train arrived!
Needless to say when the rescue train arrived there was more confusion as to what train was going where, not helped because the cardboard in the window showed where the train had intended to go, rather than where it was actually going. As the first train to arrive at Grantham for the "rescue" train I did at least get a seat, but many were forced to stand. Needless to say it was too noisy on the train to try and sleep and the lights were on full glare too which did not help.
Then once it did finally get going, around 1am, it stood somewhere between Grantham and Peterbourgh for around 45 minutes. (The guard announced 3 times we were "just arriving at Peterborough"). Though he did at least apologise a number of times and explained "I'm in the same boat" which seemed to help the mood a bit.
At Peterborough there was a second train which the guard advised anyone standing to get off and get as both would soon depart for London (both calling Stevenage). In the end both trains run through to London.
We finally rolled into Kings Cross at 3:30am. Staff had at least left more boxes full of bottles of water at the end of the platform which was much needed by me. Then to cap it all they had closed all the exits from the station except for one, at the far side, on the road between St Pancras and Kings Cross so there was then a scrum to get through the door. I gather there were very long queues for taxis.
Fortunately for me due to engineering work on SWR I had opted to drive to Morden tube station instead and with the night tube running I at least didn't have to join the taxi queue in order to get back home or I'd probably not have made it until it was light again. Though I did have to top up the parking which thankfully you can do by phone (perhaps not necessary as I doubt anyone checks overnight, but it would have really been the icing on the cake to have got a parking ticket, too).
So yes I'd only echo other comments here that VTEC really need to handle this better. It seemed that no one had much of a clue what was going on and each announcement seemed to contradict the other. Leaving people stuck on trains for 3 hours with no refreshment available is not on and it was clear Grantham could not handle the number of waiting passengers at that time of night as it was by then quite cool and only a small waiting room.