Planning a trip to Huddersfield the other day, I happened across the nearby villages of Linthwaite (pronounced lin-fit) and Slaithwaite (pronounced slow-it, or slaw-it depending who you ask). Thinking this strange I looked into the matter and turned up Seathwaite (pronounced sea-wait), and also Bassenthwaite and Hawthornthwaite, pronounced as you would expect. I have been unable to turn up any guide as to how Haverthwaite, Hampsthwaite or Thornthwaite are pronounced.
I realise that the pronunication of place names surpasseth all understanding, but my question is, are the three odd pronounciations the remains of an older form? If so, how came their names to be spelt that way? And if not, is there any reason those particular names are corrupted and not others?
I suspect it isn't just a matter of local accent as Seathwaite is quite a way from Slaithwaite and Linthwaite (which are quite close together). Is there perhaps an isogloss for this?