What aircraft is this one ?

A KC-135.

It's a USAF tanker

Looks like an RAF Squadron or station badge on the fin?

Of course....

This is the KC-135 R model with the CFM56 turbofans

I see it also has the MPRS Multi Point Refueling Sysfem pods under the wings so it can deploy the "probe and drogue" system as well as the standard USAF flying boom on the centreline

I don't know how common MPRS installations are

The Multi-point Refueling Systems (MPRS) modification adds refueling pods to the KC-135's wings. The pods allow refueling of U.S. Navy, U.S. Marine Corps and most NATO tactical jet aircraft while keeping the tail-mounted refueling boom. The pods themselves are Flight Refueling Limited (FRL) MK.32B model pods, and refuel via the probe and drogue method common to USN/USMC tactical jets, rather than the primary "flying boom" method used by USAF fixed-wing aircraft. This allows the tanker to refuel two receivers at the same time, which increases throughput compared to the boom drogue adapter.

Via wiki

Edit - Perhaps only 20 in the USAF, and just 4 at Mildenhall

;UT AQUILAE VOLENT

That Eagles may fly