I have a A3 3.2 Quattro Automatic. Would it be possible to wheel spin this car in dry, warm conditions from standstill?

should not.. maybe your haldex clutch is disabled, thus the rear wheel will never engage. If it is serious, ESP light will stay on, but otherwise, you won't know. Plug in VAG-COM to read the fault codes.

To cut a very long story short, a Community Support officer made a "dangerous driving" allegation I "wheelspun" my car. He claims the front offside was wheel was spinning.

I have tried to replicate spining my wheels (on private land), but to no avail. I thought it was not possible to spin a 4x4 wheels, and also it being a automatic would not help either.

you could possibly spin your front wheel a tiny little bit before torque is transferred to the rear wheels.

as for other scenarios, With ESP off, it is possible to spin one wheel in the front axle and anther wheel in the rear axle, thus your car. example is one side of the car is on loose gravel. if you floor the car, the tires on the loose gravel will spin while the other side don't rotate at all.