In message , Paul Scott
writes

Network Rail's press release shows the track work in progress, I can't
work out from the pic if they've laid two tracks or just the one. Can
anyone clarify?

I doubt that "normal service" could be restored with single-line working
so, while it is difficult to be sure, it looks to me as though they have
laid one new track on the south side, which will become the temporary
down line, and they are checking the gauge of the old down line, which
will become the temporary up line.

If I'm right this presumably means that the infrastructure damage is
limited to the arch on the north side (left side in the latest photo),
and that it has been determined that the rest of the tunnel under the
line is OK.

--
Paul Terry