"Erm" is for the speech impedimented.
The correct usage is "em".
"Erm" is used by people with the RP speech problem. Even HM the Queen has largely got over that one. I think it was most widespread in the remote south east of the country - perhaps south of Cambridge and west of Oxford.
If you hear someone saying erm, see if you can notice other mispronunciations. My favourite is their habit of making so many of their vowels the same as in "her".
Biting the hand that feeds IT
