I had thought about fitting an alarm/immoboliser, and was hoping to fit a motorbike imoboliser, as seems ideal and not too expensive.
http://www.motorbikealarm.co.uk/
May be some ideas here for you.
I had emailed an enquiry and got this response. Was about £30 I think, I imagine they are upto scratch regs wise.
We get quite a few buying for kit cars to be honest.
I would recommend one of the Cyclone V2 types ( or advanced V3 if you need the proximity sensing and paging functions )
When you order please remind us that it is for a kit car.