Thank you amondg & chempat for the information. Yes, I did know about Hilda's marriage to Knott. Hilda S. Humphreys married George T. Knott in 4th Qtr 1945 in Blackpool RD.
Septimus married a second time in June 1945 in Lancaster, to a Joyce Billsdon. So it appears likely that Septimus, Hilda and Stephen moved to Lancashire from Hendon, possibly together, sometime between 1939 and 1945.
Yes, I will think about applying for Stephen's will.