Locals know how to pronounce the names of places, because they've often heard other people say them. Outsiders often get them wrong, because they rely on the spelling, which may be ambiguous and misleading.
Yesterday’s parliamentary debate on the collapse of the carbon capture scheme at Longannet was a case in point. Dictionaries will tell you that there is no ɡ in the pronunciation of this name. It is lɒŋˈænɪt (with appropriate possible variation in the exact vowel qualities). I don’t know the etymology, but this suggests that it consists morphologically of long plus Annet. The lack of phonetic g is parallel to its absence in long odds or long overdue. The only people from whom we would expect a velar plosive are those with the local accent of the patch of northwest England in which singer rhymes with finger.
But as I listened to Today in Parliament (BBC R4) yesterday evening I noticed that Chris Huhne and other MPs were calling it lɒŋˈɡænɪt, as if the second element were gannet. Huhne was born in an ‘affluent’ part of London and attended the fee-paying Westminster School. So an RP speaker, then. (It appears that his mother was an actress who supplied the voice for the speaking clock.)
There’s a good television clip here (sorry if it’s not available in your country). On it you hear both the Scottish reporter, several times, and a local manager pronounce Longannet without g, but Chris Huhne pronounce it with.
Another Scottish -ng- trap is Kingussie. It looks as if it ought to be kɪnˈɡʌsi (or kɪŋ-). But it isn’t, it’s kɪŋˈjuːsi. According to Wikipedia, it’s from Gaelic Ceann a' Ghiuthsaich ˈkʲʰaun̴̪ ə ˈʝuːs̪ɪç. (I think that’s a better order for the diacritics on k than the kʰʲ you see in Wikipedia: the palatalization applies to the whole initial plosive, aspiration only to its release.)
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Here's Paul Kerswill in today's Sun newspaper. An excellent example of the "impact" our paymasters now want English academics to achieve.