Well, I've read it and signed it. I agree in principle with the idea though, but as usualHM Govt demonstrate a thorough lack of understanding when applying legislation to anything.
As historic vehicle are effectively tax exempt, the sentiment is that they are preserved vehicle of historic significance, not some tricked-up super modified competition vehicle the owner is simply too tight to pay road tax for. If the vehicle as it exists bares no relation to the original vehicle then in my veiw it is not a historic vehicle and shouldn't be classes as such.
But then I don't think any older cars should be paying road extortion tax anyway.