Why do British speakers pronounce “ma'am” like “mom”? How do they pronounce “mom” then?

The problem here is that we English speakers are trying to deal with a question that’s been asked by a person who is very unlikely to speak the same vowels as us.

One answer explains that ‘ma’am is pronounced ‘marm,’ (which would rhyme with ‘calm’) - the questioner will very probably pronounce that ‘mahrrrm’ whereas we actually pronounce it more like ‘mahhm’. Police officers in the UK address inspectors, or female senior ranks, as ‘mahm’ but the Queen is most definitely ‘mam’ rhyming with ‘ham’ which is only reasonable given the fact that it is short for ‘madam’.

The problem with this, howeve...