S type diesel brakes

[Alistair Stuart]

I have recently purchased a 2007 S Type 2.7 diesel automatic which has a braking problem that my mechanic is scratching his head over and I’m hoping someone here knows the answer. When braking, the pedal is initially hard with no retardation, press harder and the pedal goes down and the car stands on its nose. When you release the pedal, it stays down initially but slowly comes up allowing you to drive off, but works better when you put a toe under the brake pedal to lift it fully.

So far my mechanic has stripped all 4 corners and reassembled, changed the brake servo and also the vacuum. Still does the same with the added benefit of now showing an ABS fault.

has anyone else experienced anything similar, or understand what is going on?