"the intention was to dual-carriage that stretch"
There in the early '50's a stretch of the A1 around Stamford (I think North of) about 5 miles long on the West side of the single carriage way which was in a more advanced state of readiness than your stretch Danny.
Development varied between just fenced to several unlinked sections of 200 to 300 yards long completely surfaced. Apparently work had started in 1939 but had not yet recommenced.