Speculation
There is a birth for Montague I. GOODMAN , mothers maiden name JENKINS, in Holburn, 4th quarter 1926.
In 1939, there is a schoolboy, Montague COOK, who on 15 Nov 1947 changed his surname to GOODMAN. He is living in the Patterson Household, in Cumberland. His birthdate was in Oct. 1926.
If this the right Monty, I am wondering if he was born to Miriam and Harry Cook, but for some reason, Leslie was under the impression it was his?
Or did Miriam and Leslie meet up again after she sailed back to England in 1924?