2002 Vauxhall Corsa vauxhall corsa brakes vibrating when breaking at 70mph+

I have a problem with my break pedal vibrating when breaking hard at 70MPH+, My mechanic has changed and checked everything, I have had new discs and pads, ball joint, steering rack shaft, balancing, etc., etc, but is still there, there isn't any play whatsoever in anything.

The car does not have ABS, it has drums on the back, the run out of the discs is ok, 0.0015" it feels like it's coming from the front. The vibrating is very noticeable on the break pedal, not so much through the steering. The wheels have been re-balanced even though they were only 10g out. It is the same with a different wheel on the drivers side but I haven't changed the wheel on the passenger side, they are alloys, I don't know if they are better or worse than steel.