Front-end vibration

[Diablo]

I have a 2005/6 A8 3.0tdi. Recently, I have noticed the following:

When braking from 60mph+, moderate brake application result in a lot of vibration in the steering wheel and the front end generally. I think I can also feel the brake pedal pulsating a little.

When braking from 60mph+, heavy application of the brake pedal results in less vibration in the wheel and front end.

Slow speed braking is fine.

My mechanic changed the pads from Red Stuff (fitted by previous owner) with Pagid ones. It has not really made much of a difference. I suspected the discs, but the mechanic, who has not taken them off, reckons they are ok and that a wheel bearing may be worn.

I suspect that the front disc/discs are warped. Does anyone have any ideas??

Thanks in advance.