I would walk away, QUICKLY!
If they have that attitude before you buy the car what are they likely to be like if you have a problem. There is absolutely no legitimate reason not to give you the information you asked for. Sending the AA to check the car is a no risk situation for the dealer, if there is a problem there's a chance that the AA may miss it and the dealer isn't out of pocket, you are though by about €300 if I remember correctly.
I've never had a garage refuse to let me send the AA or mechanic as its no loss to them but I've had some refuse to bring it to a mechanic, it costs them time and a small amount of money, so if they show reluctance at this its likely the mechanic will find some issue, one the seller is probably aware of and knows will be found.
Once again, I'd walk away but ask to speak to the garage sales manager and tell him why, their sales staff are only encouraging mistrust.
D