In an attempt to answer my own question, posed in #2474, about the eastern Bristol tunnels, I had another look at the NR project updates for the area. They have two, one is for Bristol and the other for BANES. The latter only mentions the Keynsham track lowering work, recently completed. The Bristol one, only updated two days ago on the 26th, mentions, as follows:
"Bristol East Junction
In preparation for the new fleet of electric trains, we will be re-modelling the junction to
improve the track layout and reduce congestion.
Upgrading the track in this area will support the provision of additional fast train services
between Bristol and London"
So a gap on anything between there and Keynsham. I assume thus, that there is no preparatory work needed. That surprises me as, although the short tunnel, No 2, at St Annes is cavernous, about 30 feet tall at the roof apex, I did not think the long one, No 3 Foxes Wood, was. As in the case of Box Tunnel, I thought it was only huge at the entrances.
Any inside knowledge about this?