I did this a few years ago in my Mondeo ST220.  It was a lot of fun, but I wouldn't choose silverstone for a normal road car again.  After only a few laps the brakes were totally cooked, clutch was slipping after 20 minutes because of the heat and the car just didn't really appreciate it.  I know the GTi is a smaller lighter car, but silverstone is just to big, fast and open to really enjoy a 200-230bhp hatchback imo - you need a circuit that's tighter and windier to really appreciate the values of the golf.  It was feel slow and lost at silverstone I think.