Again, sorry if this sounds a bit thick... but...
the Bedpan line should have approx 16 TL trains/hr and MML runs 4 or 5... meaning 20 trains per hr... now the incident took place at 6am... so in 2 hrs that's 40 trains involved... 50 miles of track {BedPan line is 2 tracks in each direction} now I'm pretty sure that there is a signal more often than once a mile so I think some serious questions should be asked how the service on the GN lines fell apart so catastrophically... to me, and I'm sure to many passengers who are lay people, it just seems that TL found a particularly convenient excuse to say "not our fault the service is a shambles" this morning
Having had a quick look through RTTT, it seems trains were losing massive amounts of time in the core. It's hard to say how much this might have been exacerbated by the ongoing crewing "issues", however it certainly doesn't bode well -- but, and sorry to keep repeating, lest I be accused of being a broken record, there are plenty of people here who will join me in saying "we told you so"!
In essence, you're absolutely right that a signal failure at Luton shouldn't be disrupting Peterborough. Unfortunately, thanks to the Thameslink Programme, it now does. Politically I think that will become increasingly unacceptable, even more so than it already is. Quite simply there will have to be a re-think of the GN side of things so that there is a reliable core (and I don't mean core as in Thameslink core!) service to every destination. In practice this means a base service of 1tph KX-Peterborough, 1tph KX-Cambridge (semi-fast), 1tph KX-Cambridge (stopping), 1tph KX-Kings Lynn (fast), plus the inners of course. All the better if we can utilise the stored 365s and send the displaced 12-car 700s to uplift capacity elsewhere, bearing in mind plans have changed since the 8-cars were ordered for the abortive Caterham/Tattenham Corner service.
As posted elsewhere, I know exactly what I'd do. 365s for hourly Cambridge/Peterborough, take the 6x387s used for the Peterborough peak fast service and use them to expand at least two Baldock services to 12 cars (would have to find a solution to how to reverse them), backfill the 387s with 365s and a 700 or two to make up the numbers, and send the remaining 12-car 700s to the Rainham service, leaving a very small number of 8-car 700s spare. If the wind was blowing the right way I might look at whether the 1tph KX-Ely service could become a ThamesLink/ service, but again there would be some infrastructure and political issues to work through (running 12 cars north of Cambridge, are there enough 700s, and Kings Lynn not getting 2tph). If all the above could be achieved, this would mean:
* At least an hourly KX service to every GN outer-suburban destination - so greater reliability for those who need it
* More off-peak seats (365 vice 700) and superior rolling stock (e.g. more legroom, more sideroom, tables, etc.)
* More peak seats on the fast Peterborough services (365 vice 387)
* More seats and extra standing capacity on 2x high-peak Baldock services (3x387 vice 2x365)
* More seats and extra standing capacity on selected Luton-Rainham services (FLU vice RLU)