To cut a very long story short; the head is a "character". A couple of years ago the LA wanted to close the school as there are hundreds of empty desks in the authority and a large proportion of the pupils at the school came from neighbouring areas (parents living closer preferring other schools in the city). Head had also refused to go coed, which meant that another school which wanted to go coed couldn't do so. There was a lot of unmet demand for coed, non-denominational school places.
Head evaded closure by taking advantage of the government's policy to allow schools graded as Outstanding to convert to academies (although they had to start admitting boys, which at least allowed the boys school to admit girls).
Ofsted report not long after gave another Outstanding. Then a little over a year later, in December 2013, the school had a surprise Section 8(?) safeguarding inspection. This became a full inspection, which concluded mid-December 2013.
The safeguarding inspection report has been published, but the full report has not. Neither the head nor Ofsted are saying why. The whole thing is extremely fishy and it's not something I've heard of happening before - this isn't just a case of a school challenging a report, from what I can see.
Sorry that's way longer than I hoped 
The local paper is all over it but I've seen nothing in TES or elsewhere:
Local news article - one of several!