I think that OFCOM would have noticed an unlicensed 1.2kW transmission, they're pretty capable at this sort of thing. They've got quite a nice pile of kit for spotting troubling / unauthorised transmissions, and have statutory powers and duties in this line. An unlicensed 1.2kW transmission (which is quite a BIG signal after all) would certainly raise eyebrows on even the most casual of official observers. Is it possible that your information about his license is wrong?
Sadly that is not the case. Ofcom, with amazing resources at Baldock and many remote monitoring devices, rarely acts in these matters unless paying spectrum users, military and emergency services complain. It is not the good old days of rigorous spectrum enforcement as we had with the GPO.
Day in and day out, many novice radio amateurs in the UK breach their licence conditions by varying magnitudes, a large number using 100w transceivers at their full power, a small number using external amplifiers of in excess of 1kw output, the maximum for full licence holders is 400w in the U.K.
Many countries place easily enforceable frequency use restrictions on their novices, in the hope these novices will progress through the license structure, where-as the U.K. chose to have power restrictions that cannot realistically be enforced. The majority of novice radio amateurs in the U.K. know they can effectively do whatever they want without any chance of license revocation.
The gentleman in this case is a novice (foundation licence holder), he has an MI3 callsign, and a restriction of 10w.