Hi. Just a bit of useful info

Had an A3 2004  8P1 (2.0 tdi) and the battery went flat. The door lock also didn't operate with the key, probably because it never got used due to always using central locking.

The way I got over this was to jack the front of the car up. Remove the shield under the car, Remove the cover from the starter motor and connect the positive clip of a jump lead to the positive lead on the starter motor and the negative to the engine block. I then connected the jump leads to my other cars battery and operated the remote control. This allowed me to open the bonnet and re charge the battery.

You could also do this with a jump start battery pack.  

Hopefully this will help someone else out.

That's a neat trick Kevin, though it sounds too much like hard work for an idle bugger like me. When it happened on my wife's car I took the lazy way out and squirted penetrating oil into the lock barrel and just left it for an hour or two. That freed the barrel enough to let me unlock with the key. Needless to say I then squirted some real oil into all the locks for long term protection.

Actually good point to take from this is do we ever take the time to endure the drivers door lock is free in the first place. 

White grease aerosol is great for keeping a lock free. Diesel is a very very good penetrant for a seized lock if WD40 doesn't do it.

I did try penetrating oil and wd40 as it happens, but neither worked. The lock just would not budge. It's just lucky the starter motor is quite easily accessible once the shield is removed.