Hi all!
I just finished a return transatlantic trip using UA -> bmi. In all reality I think 20 - 30 mins to disembark, go through immigration and then get that stupid bus to terminal 1, and then go through security is reasonable. However be warned I was talking to a gentleman in the security line who said that he has had to wait upto 30 mins in the security line alone, and some of the muppets that work there...
Bottom line, leave plenty of time. However if you're *G the bmi lounge is very nice so it's something to look forward to at the end of the ordeal.
Safe trip