This thread appears to have been reinvigorated somewhat since the news that the 'JP incident' at the Southport Display is also being looked into as part of the ongoing inquiry. A fair mixture of views have appeared with the usual (for PPRuNe) spread of overly aggressive posts from some. The dynamics of the display sequence have never been too far away.
Turning to the 1/4 clover/loop debate; I have to opine that it was neither in its pure form, but rather (as the AAIB stated) a rolling and pitching manoeuvre. A pure 1/4 C with a 90 roll once in the upwards-vertical is followed by 3/4 of a loop and does require a lot of height at the apex. Now albeit a little lighter, the similar power/weight ratio of the Hawk flown at GH altitudes needs about 4000ft to complete a loop from a level 300kts entry, reducing to about 160kts over the top. In the thicker air lower down when display flying I dare say an 'aggressive' loop could be completed in 3-3500ft, but certainly not 2600ft that the Hunter is alleged to have peaked at. Even the JP/Tucano used about 2000ft of sky.
The change of axis required after the Hunter's initial flypast and Derry Turn at Shoreham could equally have been achieved with a variety of profiles; a 1/4 clover; a skewed loop (a touch of roll input during the manoeuvre resulting in a noticeable heading change); a modified barrel roll where the pitch rate somewhat leads or lags the roll rate again resulting in the aircraft exiting on a noticeable different heading to that upon entry; another Derry Turn / Canadian break. I'm sure most of us in the military have at some stage flown these 'skewed' loops or barrel rolls quite unintentionally - I know I have. (I can still hear the Wonderful Bill Brewer sat next to me to this day!)
Now, any manoeuvre terminating in a significant looping element (like the 1/4C) needs the corresponding amount of vertical space for successful completion, but a modified barrel roll could produce the required change of heading needed with a lot less of a vertical displacement. The required gate heights (ignoring IAS) could probably be between 3600ft for the 'loop' down to as low as say 1500ft for the 'barrel roll'.
I don't know what Andy was attempting on the day, but it appears from the video that the Hunter, once inverted, was effectively trying to complete the last half of a loop with very little if any change of axis, hence roll. He may well have achieved the planned gate height if he was planning on being at the apex of the manoeuvre off-axis and hence pitching and rolling (i.e. barrelling) out onto the A axis where much less altitude is needed. However, whether he momentarily lost his SA (dazzling sun, A27 v rwy 02/20) or he simply misjudged it, he was left with insufficient height to complete the half-loop manoeuvre with such tragic consequences.
I'm afraid you may well need to get your hands out to 'fly' the profiles elaborated on above, and as a QFI I have little doubt the QWI(s) will already have left the bar and gone to bed or fallen asleep in the corner!!!