I have an idea Zazur that might help.
When I visited Sally and Steve at Melton Tyre and Exhausts, Steves mate came along in his Corsa VXR.
He said he had a squealing problem with his brakes and that the pads weren't even worn down.
Steve then suggested to put it on the ramps and he'd have a look.
He removed the wheel (front) and removed a brakepad to examine it.
He then noted that the area on the pad that comes in contact with the carrier was dry and needed some coppergrease on it, and also the same area on the carrier too.
Reason for this is that where the pad and carrier contact, there is slight movement, and if there is no coppergrease there, it's metal grinding on metal, thus making a squealing sound.
He greased teh contact areas on all four corners and Owen took the car out for a spin. Returned with a smile on his face as the squealing had gone.
Maybe this is worth trying. You might be able to see where the contacy areas are as they should be shiny because no grease is there.
hope this helps