we don't, but the USAF does...
the USAF might well be happy to provide tanking support to the UK C-17/RC-135/E-3/P-8 fleets when they are providing take to the US, or doing something the approves of, but what about when they are doing UK sovereign stuff that the US either doesn't like, or doesn't want to be seen to like?
anyone want to take bets on whether the US would provide tanking to RAF RC-135's snooping around the Argentine coast from Ascension, or to C-17's flying Apaches or GMLRS down to Mount Pleasant?
or is the UK sovereign stuff just less important than all the US-lead ops in wherethe****istan?