My late father, who was born in Somerset in 1909, used to say that as a young child he remembered a very elderly great aunt, someone probably born before 1850, who was "a bit posh". And she pronounced Cirencester "Sissiter". I know there's been some other reference to this on this site: I just thought I'd add my pennorth.
I haven't heard that, but I have heard it pronounced Sissi s ter'.
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