My late aunt lived in a village on the edge of Doncaster called Bessacarr. You’d think it would be pronounced ˈbesəkɑː. But you’d be wrong: it’s ˈbesəkə.
The weakening of unstressed vowels is one of the trickiest areas in the pronunciation of British proper names. Those who first encounter them in writing tend to make them strong, while those who have local/personal familiarity with them know to weaken them.
The town of Todmorden in the Pennines (pictured) is most usually ˈtɒdmədən or just tɒd, though you can also hear ˈtɒdmɔːdən. (According to Wikipedia it can also be ˈtɔːmdn, though I rather suspect that this is no more than a Wikipedia contributor’s joke, particularly since English phonotactic rules would require an extra schwa, ˈtɔːmdən.)
In North Yorkshire there’s a village called Dishforth. It has an RAF station generally known (I think) as ˈɑːr eɪ ef ˈdɪʃfɔːθ. But the locals call their village ˈdɪʃfəθ.
I was at school with a chap called Spofforth ˈspɒfɔːθ. But the village of Spofforth near Harrogate is ˈspɒfəθ, which according to the BBC Pronouncing Dictionary is also for that matter the usual pronunciation of the surname.
Most English villages called Marden are of course ˈmɑːdn. But the one in Kent is also sometimes mɑːˈden.
Spelling pronunciation is a powerful influence. The place I know as ˈæskət, Ascot in Berkshire, is often heard as ˈæskɒt.
Even in America things are not necessarily as you might expect. Think of Poughkeepsie pəˈkɪpsi.