On Ethels link, the main thing it has to pass is the SVA test which is like an MOT on steroids! I believe over 75% of kit cars fail this first time. After that its all pretty straight forward.
Unless things have changed recently, you can drive a kit car to a VOSA test station without registration plates as you won't be issued with a number until it is registered and you can't register it until the test is passed. You must however have insurance which can be obtained using the VIN number.