The Royal Air force has been in the RC-135W business since Nov 2013 when tail #ZZ664 was produced by L-3 Communications at Majors Field (see USAF news here). The 2nd aircraft, tail #ZZ665 was delivered in 2015 (see FlightGlobal story here). The 3rd aircraft (ZZ666) is scheduled for late 2017. Three aircraft were purchased from the United States under the "Airseeker" $988 million dollar contract. All three aircraft will be regular visitors to Majors Field for "baseline" upgrades through their lifecycle.
The aircraft are actively supporting operations in the middle east according to the Aviationist (see May 2016 Libya jamming attack article here). Note the aircraft is not really configured as a jammer, but does have numerous radios in the HF, VHF, and UHF bands that could be used to disrupt known frequencies ISIS uses by simply transmitting any garbage the crew chooses to put in the microphone or possible a secondary modulation input.
The 2nd aircraft, tail #ZZ665, on the L-3 Communications flight line at Majors Field.
ROYAL AIR FORCE RC-135W PROGRAM