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 has amazing resources at their disposal via Baldock and a surpsingly large amount of remote sources , but they are not utilised for licence breaches within the amateur radio bands. And unless other 'paying' spectrum users, military and emergency services complain, Ofcom will rarely act.
The number of 'novice' radio amateurs breaking their licence conditions by exceeding their maximum power output is huge, many using 100w, some 1kw, a few are using even more than that.
Where-as many countries have frequency restrictions on their novice radio amateurs, in the hope they will progress through the licence structure, the U.K. elected for power restrictions which cannot realistically be enforced, and these novices have no reason to ever progress, they can do whatever they wish without any fear of licence revocation.