Edit: You get a basic 2007 spec 3 door GTI for £17995 with ANY

transmission - manual or DSG box

Presumably these are pre-registered cars with delivery miles only.
The ad also quotes that price for a 2008 model order with a 3 year warranty and delivery prior to Christmas.
No doubt a 2008 model will cost more and extras will bump up the price but the current VW dealer price is £20607 for the manual and £21937 for the DSG respectively.
No VW dealer will get anywhere near that discount on a new GTI built to order.
Cass