SSL access to Liverpool Street Mainline Station

They did use a tunnel, part of which is still there and used for staff purposes.
The track access was through platforms 1 and 2 of the old station, but was long gone before the rebuilding in the lates eighties/early nineties, although for many years access from the concourse to platform 1 was only possible from the footbridge

The intention was I understand to run Metropolitan trains through to Chingford.

So the Met would almost have been Crossrail 1?

There is a photograph of the Liverpool Street end of the tunnel. It was published in a special edition of British Railway Journal(GER) about 20 years ago. The GER society may be able to help.

The very first photograph was taken from the footbridge that used to give access to platform 1 that crossed the mouth of the tunnel.
Correction, the second photo.

What a fabulous set of photos! Thanks for sharing, Nigel@Hornchurch.

Shed apart, the old station as I recall was, from the passenger point of view, a dump. There was no proper concourse, and the circulating area was divided in two by Platforms 9 and 10 extending almost to touch the Great Eastern Hotel, as can clearly be seen in one of the photos. To move between the sections you either had a long detour through a pinch-point, or over a footbridge - both highly inconvenient, especially with luggage. The approaches and facilities were grey, dour, and very depressing.

The rebuild created a huge, bright, airy concourse, preserving and restoring as much or the original as feasible in a modern context. The shed itself with its magnificent roof has been superbly restored. The station to my mind is an excellent example of harmonising the best of historic architecture with a pleasing, functional, modern environment.

Granted King's Cross and St Pancras have now stolen the crown for restoration-with-modernisation, but that's progress.