Terry Harper wrote:

Somewhere I have a brochure produced in 1938-9 to promote
industrial estates in the Forest of Dean and Chepstow area, and
that shows a dual carriageway road tunnel under the Severn, running
almost on the alignment of the now A49 and the first Severn Road
Crossing.

The A49 route is Ross-on-Wye/Hereford/Shrewsbury/Warrington/Preston
(nearly). I assume you mean almost on the alignment of the original M4
Severn Bridge, now M48.
--
Richard J.
(to e-mail me, swap uk and yon in address)