Isn't there a connection at Calvert?
https://www.hs2.org.uk/building-hs2/trains/calvert-infrastructure-maintenance-depot/
Not for passenger use, but potentially useful for construction once the tracks get that far?
It’s been simplified, there was going to be a south to east route, (Southern Access Chord), into the infrastructure depot sidings, with a skew bridge under EWR, but that was dropped. The only connection now will be off the southbound HS2 into the infrastructure depot, and then through a connection at the east end of the depot onto the eastbound EWR, with a couple of loops alongside EWR.
It was discussed a few months back in this thread, but was in a presentation linked in post #323 here, I think most people missed it first time it appeared:
There used to be 3 or 4 footpaths crossing the railway between Launton Bridge and the old Launton station. Does the one footbridge serve them all? Looks like it - I can't find a really nice set of docs that were around last year, but this map has the detail: Network Rail rights of way doc
www.railforums.co.uk
It’s a bullet point towards the end of the presentation, about pages 24/25 of 30.
“The Southern Access Chord into the IMD (an additional length of track) has also been removed to simplify the construction process.”