In a previous post, you mentioned that you had the 1954 marriage certificate.
What is Robert's occupation? And is his full address given? Is he a bachelor?
In 1939, there is a Robert J Lethbridge (DOB 4 Aug 1909) in Ottery St Mary UD. Occupation market gardener. Partial address: 5 St Saviours. Marital status: single.
He is with Arthur W and Elizabeth A Carter.
Ottery St Mary is within Honiton reg dist (the district where the marriage was registered).