Many thanks for those. I was interested to read about the autotransformer provision. Can someone please remind me whether any of the already-wired section of MML is currently equipped with ATF?
Currently, only the section between Kentish Town SATS (Sectioning Autotransformer Site) & Borehamwood ATFS (Autotransformer Feeder Station) is equipped with ATF. This was done as part of the Thameslink Programme works.
The new TSCs at Napsbury (KO1a), Ampthill (KO1), Bedford (KO1), Irchester (KO1), Harrowden (KO1) and Kettering North (KO1), along with the MPTSCs at East Hyde (KO1a) and Sharnbrook (KO1) are all autotransformer ready. Long Meadow Farm (Chalton) ATFS (also KO1), which came online last Christmas, also has AT capability, and Braybrooke ATFS (KO1a) will have it from the outset.
IMO it makes sense to do all the work, including ATF, right now on the Kettering - South Wigston section as the contractors won't have to come back to retrofit it later, on a section of route without the ability to keep one pair of tracks open.
Further west, the SPL teams were hard at work installing ATF insulators around bridge SPC3-35AA (Braybrooke Bridleway Bridge) - see pictures below.
I arrived around 3pm, just before sunset; at this point, the team had just finished installing their 5th pair of insulators on the TTCs in the area. They started their 6th pair as I left, and are probably complete through there now. They seemed to have missed out the MPA Portal in the area (SPC3/129.070/DM+UM), but they might have returned to it today (11th December).
Trial Holes have also been dug for the northern ATF Anchors on the other side of the footbridge. The existing SSA piles to signify the southern end of the next run of wires, numbered SPC3/129.439/DM+UM, now have holes 5m north, at 129.444km. (The UM hole has Armco Barrier next to it.)

Earlier that day I also checked around Judges Bridge, Desborough (SPC3-38) - piles and Armco Barriers (on the DM side) for the new ATF anchor masts either side of the bridge have gone in now too. There are also 2 pairs either side of SPC3-37F (the A6 Desborough Bypass) but it's impossible to get a snap there unless you're on track!

ATF insulators have also reached Market Harborough, although only around U/B SPC3-31 (Scotland Road), and only on the southern anchors and both TCM pairs. The big monoboom Anchor (the Series 1 Portal) looks to be anchoring the ATF on the DM side - couldn't speak for the UM on this trip.
Update 12/12/22: Trains still running via the Corby route all day today as one of the engineers' trains derailed yesterday.
As of 1445 today, the engineers' trains are all still on site...
(Images show the line block still being in place between Kettering and Wigston Junctions)