[daedalusminos]

Ok, just thought I'd post how this 'ended'.

Getting to the thermostat was relatively easy:
No need to jack car, though it would make it easier to replace under tray.
Remove engine under tray (turnbuckles - 3 front, 3 rear and 2 each side in front lower wheel arches)
Drain block LH: drain pipe runs down LHS of engine to sump level. Remove expansion tank cap to allow max drain - expect about 5litres.
Move drain container to front of engine ready for a small amount from behind thermostat cover.
Remove timing belt covers
Remove 4 bolts and loosen one behind RHS cam wheel to allow pressed metal TBelt backing plate to be swung up.
Pull Tbelt half way off RHS cam wheel (use cable ties to ensure it doesn't come all way off)
Loosen and remove 3 thermostat housing bolts (prepare for small amount of coolant loss)
Pull housing forward and slide up allowing thermostat and O-ring to be removed.
Reverse procedure to replace. Don't forget to remove cable ties!)

L/RH as seated in driving seat.

Important points: the thermostat I purchased from local motor factors was INCORRECT! The correct thermostat is 67mm, 82°C (the bypass valve flap was also the incorrect diameter)......in the end I went Audi genuine part.