£500 extra for a slightly older, but much better, better-handling, faster car.
... assuming he doesn't crash it (or someone else crashes into it) - at which point we hit an obscene amount of money that'll be more than Year 1. Remember you're recommending a 21 year old whose regular driving experience consists of a Corsa gets an old (possibly rear drive, such as the 200SX) Japanese 7-seconds-to-60mobile. I know he wants an A3, probably a 2.0 FSI, and the car that falls into that model and price bracket has (
according to Top Gear) a 9.2 seconds to 60 time, FWD and 132mph top whack.
Personally, in Poverty's situation, I'd just buy a Mk1 MX5 - the slowest being 9.4 to 60 and 119mph top speed,
according to Wikipedia - and have an absolute riot in it. But then that's just me.
.......
As an aside. Group 18, 3.0 litre V6, £311. Get in!
Git.

Was that quote originally Old Geezer's? I searched for it once but couldn't find it.
Not one that doesnt look and drive like a granny mobile.
Mazda MX5? Honda Prelude? Toyota Celica? To name but three. I can honestly say I've never seen a granny driving any of them. The Celica won rally championships; you don't do that by having grannymobile handling.
At the end of the day, you seem dead set on getting an A3 and nothing anyone says will change your mind. If you're prepared to pay for it - and paying is what you'll be doing a fair bit of, and none of the figures will be small - then buy one. But don't expect anyone to notice you - unless the ability to stay inconspicuous is what you want from a car, in which case I can't think of anything better than an A3.
Or you could always get a Mini

Cheap to run, insure, has handling to put a grin on your face, and in London you'll be able to park it anywhere! Just a thought.