Andy wrote:

I'm not sure why the off-peak joint TL/SER services would have to run
ECS to cricklewood sidings. There is spare platform capacity (4
platforms, 6 tracks) at Kentish Town and the current SER service is
only every 30 mins.

There is no access to the Fasts or (I think) the Up/Down Slow from the
Moorgates until after you pass Kentish Town in the down direction, so
that alone whittles it down to 3 platforms/tracks. And that assumes the
Moorgates are adequately bi-di signalled, which they are not.

Therefore I make that 2 tracks/platforms available for use.

Running ECS to cricklewood just moves the conflict with existing
services further north, the northbound terminating trains would have
to cross the southbound at a flat junction.

True, but your suggestion (as quoted below) does not eliminate the
problem. THC has suggested how the most can be made out of reversing at
Cricklewood sidings.

Whereas at Kentish Town, the northbound terminating trains can stop
in the current 'normal' northbound platform

The Down Moorgate is not signalled for reverse workings north of King's
Cross Thameslink so you would need new equipment for that purpose,
otherwise you would have no option but to reverse somewhere further
north (as is the plan AFAIAA). Reverse workings will conflict with down
services and then up services until they clear Dock Jn North.

whilst the northbound thameslink trains run past on the other side of
the island, as sometimes happens already when there is a service disruption.

Really? Now there's a surprise - I was under the impression that the
Up/Down Carriage was cleared only for ECS workings between Kentish Town
and Dock Jn North.

Just because the northbound 'fast' TL trains currently stay on the
Down Moorgate line through the station, doesn't mean that they have to
keep doing so from the timetable change.

Fair point. However, the crossover between the Moorgates and the Up/Down
Carriage is crap (it is limited by a PSR of 15mph IIRC); although I
don't know how the Cricklewood crossovers fare in comparison.

The other question is what happens to the imbalance in services during
the peak. At present there are more Moorgate terminators than there
are Blackfriars terminators, so where are the 'extras' from the north
going to go?

In the high am peak it's actually the other way round (9 to BFR vs. 7 to
ZMG). I see the turnback siding at Herne Hill has already been
mentioned, but it's only part of the whole picture. In any case I don't
know where exactly the peak Moorgate/Blackfriars services will go.