There’s a family tree with his death 1967. Couldn’t find him under Du Mayne Swinfield Thomas on the death index. Seeing that he also used the name Swinfield Thomas, there is a death registration Henley - 1967 for a Swinfield Thomas, age 76, making his year of birth around 1891/92, 1 - 2 years out. You could try Gloucestershire Archives, they may be able to point you in the right direction re the Gloucester Assizes.
Gloucestershire Archives
Following on from Julie's post above
This is all i have been able to access
Published: Saturday 20 May 1967
Newspaper: Reading Evening Post
County: Berkshire, England
a full report to the coroner of the circumstances surrounding the death of 74-year-old Sonning Common ex-gardener Mr. Swinfield Thomas. Mr. Thomas collapsed and died at his home Fir Tree Cottage. Bishopswood Farm estate on Thursday after being involved ...
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Published: Thursday 22 June 1967
Newspaper: Reading Evening Post
County: Berkshire, England
during a neighbour's squabble, a Henley inquest heard yesterday. A few minutes later the pensioner, retired gardener Mr. Swinfield Thomas, died of a heart attack at his bungalow
https://www.britishnewspaperarchive.co.uk/search/results
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