BA at DFW has a dreadful lounge; the J area is nicer than the F, there is no bar (or rather, the liquor is kept locked up and you must wait hours for the attendant to deign to fill your glass) and about the only good point are the UK papers that BA flies in; otherwise use the AA lounge which is J only -- much nicer, and with showers. Sadly DFW-LHR is a poorly served route by BA, not sure why but MIA-LHR has much nicer service than DFW-LHR (maybe a lack of competition?). You won't get the normal level of BA F TATL experience. If you can spare a sector you would be much better off going via JFK, LAX, SFO or even SEA than DFW-LHR. Even DTW had better BA lounge and service than DFW (!!!)