Originally Posted by
SFTNYC
While you'd have plenty of time to leave the sterile area, if you don't want to your DL gold status and AF boarding pass (regardless of travel class) will get you into the skyteam lounge in T4 (where AF departs) which has showers. Note that when transiting at LHR, all passengers must reclear security (even though you won't have to clear passport control in your case). You'll also need to change terminals, (DL uses T3, AF uses T4) but this can be done using the airside transfer busses.
The Sky Team lounge, which Delta used until it moved all of its flights to the Virgin Atlantic terminal, is two floors and very nice. The food and drinks are more than sufficient for the 3 hours you'll spend inside, assuming, in the worst case, it takes 60 minutes to transit terminals and clear security. If you get lucky, the spa may even have an opening for its complimentary treatment.
Don't forget: Delta can check your bag, if you have one, all the way through to Paris so you don't have to worry about this in London.