I have the same plan and actually for the same dates around ultimo April beginning of May.
To be honest I'm close to crapping my pants at the thought of spinning off and totalling the Boxey...and spending the rest of my life paying my bank
But on the other hand the track is where the Boxster is at its best.

I made a post about this a couple of weeks ago and got ONE answer. WOW!

Here are a couple of the links Ive found so far:
http://www.bedfordautodrome.com/
http://www.ridedrive.co.uk (sounds good)
http://www.advanced-driving.net/security.html (just for fun..hehe)
http://www.drivingtechniques.co.uk/

Check it out and let me know what you decide to do.
I might wanna join the fun...if it isn't all right-hand driving fun