Originally Posted by toothpick
Yes - when you transfer to T1, go out to the landside area where all the check in desks are. To avoid the crowds, go out the door onto the sidewalk and walk all the way down to your left, back in the last door, keep walking you'll pass by the 1st class check in, then keep going and you'll find the BA arrivals lounge.
For clarity, I think that these are instructions to go to the FCC, and then head towards T1
domestic departures (as would be expected given that you'll have a boarding pass for MAN). En route through the FCC, you will go through the inbound immigration control. After getting into the domestic departures area, follow the exit signs past the baggage carousel and then follow the above directions.