Compared to the bit of CDG from which BA currently operates (read: is forced to operate), LHR T4 is heaven.
Best thing to do, if you can, is to check in online 12 hours before your departure (24 hours before if you're already a member of the BA frequent flyer scheme, although you can't now join it if you're not already a member if you're only flying on deep discount economy tickets). That way, you can waltz into T4, pick up your boarding pass from a machine, drop your bags (if any) at the Fast Bag Drop desk and then go straight through security. Great for avoiding the queues if it's a busy time.