It was indeed RR Merlin powered - saw it flying at Airsho 2000, sounded wonderful, similar to a Mossie. So far as I know the engines were built by Rolls.
Ex Spanish AF, it was delivered to Dog Arnold at Blackbushe by Neil Williams in 1976 (?) and lived there for a while until the CAF acquired it at the end on 1977. Neil went back to Spain to collect another one for Doug Arnold in December 1977 and was lost when it crashed in the Pyrenees. Recommend his book "Airborne" which includes a chapter about ferrying the first aircraft up from Spain.