Two further tips:

1. If you find a huge queue at the BMI transfer desk at LHR, just look at the departure monitors to find out your gate and head straight over there. The gate staff (and certainly the lounge staff) can issue boarding passes.

2. Your carry ons either may or may not make it past the gate staff (much more likely if the flight is quiet). If not, they will gate-check it (goes straight down a chute to the side of the plane) and you'll be able to reclaim it in CDG. You will not have to go out to the check-in desks or anything draconian like that, so I wouldn't worry.