Labour costs to change a differential ?

Wow! On a BMW 320i one garage quoted 8 300ukp+vat labour to change a diff.
This is the garage I usually phone to get a worst case scenario type quote!

My local one is letting me source my own diff (for 150 UKP) and want approx
225+vat for labour.

The chaps I'm buying from (Quarry Motors) say they could change a diff in
one hour at a push and are surprised labour is more than 70 quid even
allowing for London prices!

Problem is the car has already been towed to my local garage so I'll have
to get a break down in labour costs from them I guess? Otherwise towing
costs may cancel out any savings looking elsewhere.

Are these 200+UKP labour costs standard for London or something?

Lordy