Help on Battery Isolator Switches

[tvrheart]

In brief: Whats the deal on fitting a battery isolator/engine cut out switch - the big red ones, in terms of regulations for competition use?

And in full: The restoration of my friend Tony's 3000M is now on the rebuild stage and as we currently have the wiring loom out we want to install a Battery Isolator Switch. Can anyone offer some advice on these as there seems to be two types around, a cheaper one which just isolates the battery, and a more expensive one which cuts the electric to the ignition to stop the engine over running. Initially the car is going to be used for road and track days but the long term plan is to do some sprinting, in which case what are the
competition rules for these Isolator Switches. If we are going to fit one, we may as well try and do it to official spec. in terms of the actual switch and its location. If anyone has any info/links to websites or just a useful opinion on this all help is gratefully received!
Cheers in advance,
Chris
P11PLE Chimaera 450
P.S. See www.tvr-3000m.co.uk for details of the restoration