If you read the thread, the main criticism is that the timetable was indeed put together at the drop of a hat on Boxing Day evening, and no one months ago considered the significant risk that the possession might overrun and drew up an emergency timetable and rostering well in advance in case it did.
There's two things here:
a) preventing the overrun in the first place, and,
b) mitigating the effects of an overrun if it happens.
The Holloway work - and every other job on the network - went through a detailed schedule risk assessment (several times in fact) that considered every potential failure, potential resource absence, potential cause of slippage etc. Every big job like this at Christmas has to demonstrate
at least a 95% chance of being handed back 4 hours before the first train service is due to operate. This is as per a process agreed with the ORR. Of course that means, in theory, 1 in 20 jobs don't make it. Actually it is a much lower rate than that, nearer 1:100. But when you are doing nearly 1000 jobs over Christmas - as this year - at that strike rate, some of them will overrun.
For mitigation, I can tell you that there was a contingency plan for an overrun on this job, as there was for every single piece of major work over the Christmas period. As an example, the work at London Bridge has about 10 different service contingency plans depending which stage might go wrong, when, and how badly wrong. Happily the first two of those haven't been needed and have gone in the bin unused. (And I have everything crossed that we won't need another 2 tomorrow morning). However, having a service contingency plan is one thing, resourcing it is quite another. It is, in theory, possible to provide fully resourced contingency plans with different rosters and stock diagrams. However it takes weeks of effort of the planners to produce each one for a big job like Kings Cross, and frankly there is not the resource available to do it on the basis that there is a 1% chance that it might be invoked. Besides, how would you tell drivers / conductors / station staff whether to come in for Plan A or Plan B (or C or D), given that the start times might be quite different? If that means they are required to be on call just in case, there becomes an issue with working hours, and again, it is a lot of potential extra cost for a 1% chance of being used.
My purely personal view is that I simply don't understand why there were 4 car units running around, nor why some services were cancelled when they weren't affected by the work. I suspect there were other factors at play unconnected to the overrun which got 'lost' within the big picture.
