Just for the record
As a journalist I really couldn't let this one pass. I contacted the bmi press office where I was initially told they had heard of the thread on pprune but their operations department had no record of the incident so they could be of no further help.
I then contacted the Civil Aviation Authority Press Office. A press officer confirmed the incident had occurred. He said approximately 15 passengers were involved and moved forward as far as row three during the take-off roll.
He also confirmed some passengers were still standing when the aircraft became airborne but denied any passengers had been banging on the cockpit door.
The CAA report states passengers were reassured by cabin crew and the captain. It also said the flight proceeded without incident.
I went back to bmi where the press office conceded defeat and issued a statement giving more or less identical details. Their press officer also denied any passengers had reached the cockpit door.