The prime minister has been making much of the Conservative party leader David Cameron's "cast-iron" promise, now abandoned, of a referendum on the Lisbon treaty.…
It's rather spoiled, though, by the fact that he seems to be the only person in the English-speaking world who pronounces the letter "r" in "iron", thus: "cast eye-ron promise." It brings you up short and makes it hard to concentrate on what follows.
Gordon Brown is of course far from being ‘the only person in the English-speaking world who pronounces the letter “r” in “iron”’. All rhotic speakers do.
What is unusual about Brown’s pronunciation, as Simon Hoggart says, is that he pronounces the word as spelt, i-ron ˈaɪ rən. So for him it rhymes with Byron and involves the same sequence as tyrant. The usual pronunciation of iron, ˈaɪə(r)n, must result from a historical metathesis by which ī rən becomes ī ərn. The r then as usual coalesces with the preceding schwa in rhotic accents to yield ɚ, ˈaɪɚn, while in non-rhotic accents, being preconsonantal, it undergoes the usual deletion, giving ˈaɪən.
The OED gives a rather more elaborate account, involving “diphthongation” (by which I think it means the Great Vowel Shift) and “syncopation”, but saying essentially the same thing.I don’t know whether Brown’s pronunciation of this word is shared by some or all Scots. Perhaps someone will tell us. It does have the advantage of making the word clearly distinct from ion.