Mabel, William Landricome, rope maker, 23 with parents David and Elizabeth is the William mentioned by Osprey who married Jane Kent (Western). I have a copy of their son David James' birth certificate, and looking more closely I can see the address is 13 Looe Street, not Love Street as I assumed.
I have a Railway Employments record giving William Thomas' birth as 5th May 1859 - given the GRO record mentioned for William Thomas Kent, mother's maiden name Western, is the Jul-Sep quarter, this looks like a match. He must have taken his step-father's surname. Thank you for finding that Maureen.
I will have to do more checking and double-checking, especially if I want to tell my father on Father's Day that he's really a Kent, not a Landricombe!
Edit: Mabel, the family information for Jane Western is also very appreciated, as it appears her status as my 3rd great grandmother is now confirmed.
I was aware of James David and David George, but the mis-spelling of Elizabeth Jane's name meant that I had missed her. It seems very likely now that she would be the Elizabeth who witnessed William Thomas' marriage - another mystery solved!
Thank you everyone who has replied, I will be tracking the leads you have dug up for some time, some of them confirming what I already knew, and this one in particular blowing my mind!