Hi Rob,
I have been thinking over this puzzle. I highly doubt that any father would leave behind a young child between 8 and 13 years old to return to England to marry for a second time. I suspect that John Barwise took Leslie back with him. I can find no passenger arrival records for John and Leslie arriving back into England and wonder if perhaps they took a ship steerage or sailed into a European port first before proceeding to England, i.e. the ship was heading to Europe and they had to make a connecting trip to England. There are no passenger lists online for ships arriving in England from European and Mediterranean ports.
On the second front, have you checked census, marriage and birth records in Scotland for any information concerning Leslie's family? I have what may be Leslie's children born in Westmoreland district between 1947 and 1960 which you can also easily reproduce on
http://freebmd.rootsweb.com/cgi/search.pl with father's surname Barwise and mother's surname Vaughan and information that they may have been another child named Margaret born circa 1939 that died in Kendal in 1999.
I also have found an indication that Leslie may have been known as Joseph Leslie Barwise and may have died during 1981 in Kendal, Westmoreland. Have you requested a search for a Will from the Principal Probate Registry either in Westmoreland or via mail from the York office?
Just some thoughts that may help.
Sincerely,
Susan