Originally Posted by gemac
Another option is to route through ORD or JFK, so you fly into LHR. You would have to leave DFW a few hours earlier.
I would agree with those who say that it is pretty much of a gamble to attempt this on the roads, particularly if you will arrive on a weekday. Realize that if your bags are transported from LGW to LHR, that would be by road, they would be taking that same gamble. You can take bags yourself on the train and on the tube, have done it many times, not my favorite chore after an all-night plane ride, but definitely doable.
I've never done this transfer, don't need that kind of stress in my life. Good luck.
regardless of the transfer method, you carry the bags.
I've done the bus transfer many times, both ways, at different times of the day. Only once it took 1:45 minutes, sometimes !1:30 minutes, but most of the time ~1:20 minutes. Maybe I was just lucky.
The trains/underground/taxi combo for 2 will cost somewhere ~65BPs, that's ~$120.
The bus for 2 ~35BPs, that's ~$65.
I don't know where the big advantage is as both ways will get you there about the same time and with the bus, no transfers and dragging luggage around. YMMV.