http://en.wikipedia.org/wiki/Cob:
"Cob, a regional name for a bread roll in the Midlands of England."
I think I've lived in the Midlands too long...
Yup, it's called a cob! My Midland roots showing there also.
My girlfriend, who is from Stalybridge calls it a muffin, which is alien to me. When she asked for a bacon muffin in my home town, she got the reply 'Sorry love, we only do chocolate ones 'ere.'
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But on topic, I use the EMT services from STP fairly frequently and have always made sure to leave plenty of time to board for that very reason. As someone else mentioned, they usually enter the platform number 15 minutes before departure, but if you know the set (HST/222) then you can go through the barrier a minute or two early to avoid the crush.
To avoid the long walk from the tube use the Northern Ticket Hall, (no good from the Circle/District lines though) come up via the walkway, below the Southeastern concourse and you're at the right end to get up onto the EMT concourse.