Yep, has to be IAM.
Track riding is good for learning machine control, but does not help with reading the road, or being aware of potential hazards.
Bikesafe is a great way of getting an insight into what advanced riding is all about. You will get a bit of classroom talk, and then an observed run with feedback, so at the very least you will get some initial feedback to be going on with, as well as have any glaring safety issues pointed out.
Be honest about your riding ability too, as you will probably be paired with another rider for the observed run.
The police consider bikesafe as an introduction to advanced training, rather than instead of. Note that Bikesafe is actually ran by the police but observers are supplied by IAM in Surrey...
I personally did the bikesafe day from Hendon and I'd highly recommend it.
(I was already an advanced rider, and an IAM observer, but wanted to do it so I could provide first hand knowledge should someone ask me about it, as well as get an unbiased assesment of my riding by someone who did not know me ).
If you feel you want a bit more than one day, then the IAM 85 quid deal is a steal. 'Skills for life' as they call it will give you as many observed runs as it takes to get you through your advanced test. I think you also get a book on advanced riding. I say I think as I also brought roadcraft and 'not the blue book', so can't remember which you get included in the price. The roadcraft book is the basis for police training, and 'not the blue book' is written by a police instructor with extra tips and subtleties to add that extra finess.
Rapid training are excelent too, but you may not get as much value for money from them at present. I'd suggest waiting until you feel more confident, and then have a day with them.
I belong to
http://www.wvam.org.uk/, who are a 30 minute trip around the M25 from you.
As the web site says, they hold their observed rides the first sunday of every month, and you need to be there for 10am.
They also do lots of social runs. For example, vvery Sunday there is a meet & go at box hill for WVAM members.
I have also done a rapid training corse, Cali superbikes, and euro superbikes, but Imo, IAM is the best bet for you to based on what you've said of your ability.
Hope that helps.
Cheers,
John.