Thank you Dawn for your information. I have a tad more information about Henry George Hull....
1. Henry was born 15 Aug 1890 at Itchen, St. Mary's extra parish near Southampton, and he married in 1911/12 to Rose Edith Blundell.
2. Henry's parents are indeed Henry & Mary Catherine Hull (Jones). Henry was from Donhead St. Mary in Wiltshire and Mary Catherine from Porthmadog in Caernarvonshire.
3. My Mum is the only source of oral history of him. The trouble is that as she wasn't born until 1942, she has no memory of him. He apparently knew that my Mum had been born-she would have been his only grandchild at the time.She's said that what she knows of him was told to her by Henry George's wife (my great grandma). She said that Henry George was living in Liverpool (presumably the ships aboard which he served were based there) instead of with her in Southampton, and that he was "carrying on" with another woman in Liverpool.
4. I cannot be sure that he was aboard the S.S Britannic in 1942-45, it was a complete surprise to my mum when I told her that he was aboard it in 1940, although she knew he'd worked on the liners. I'm going to google the Britannic in a minute.
5. Apparently when he died, the ship had left port 1 or 2 days previously and went back to port so he could be buried. Mum said that was buried in the "blue mountains" in Australia.
Thank you again for your time in trying to resolve this family mystery.