First, we are talking here about the revised MOT rules. The guidelines for registering a historic vehicle, be it a new import, a protracted restoration with a lapsed number or even a barn find, are a separate universe.
Second, relief that the MOT-exemption criteria are so inclusive is based not on joy that so many classic cars will qualify – it still seems eminently sensible to get your classic MOT'd anyway, so that an independent pair of eyes can check that it's not going to kill someone – but on the fact that officialdom isn't seeking to make life harder for those whose cars aren't quite to original catalogue spec. It recognises that 'historic interest' is about more than just forensic correctness.
That said, paranoia-tinged fears that modified classics would be banned from the road were not entirely unfounded given the much tighter insistence on factory spec' practised in some other European countries. Anecdotal evidence from car-club forums suggests that some of our continental co-enthusiasts are amazed at the outcome, and quite jealous too.
Here, then, is the gist of what will apply from next May. A 40-plus-year-old car will, if its owner so desires, be considered a VHI if it hasn't undergone 'substantial change' during the previous 30 years. That means the chassis frame, subframes and/or bodyshell, as applicable, must be to the same pattern as the original (a Spyder chassis in a Lotus Elan, for example, could cause a problem here). Axles, suspension and steering must keep to the original type and method of operation, but substituting tired original dampers for new Konis, for example, is permissible. For engines, a different cubic capacity within the same basic engine type is fine, and alternative engines originally offered in a car's range are also fine.
So far, so good. So deliberately vague, too, and no mention is made of tuning parts such as different carburetors, hot camshafts, freer-flowing exhausts, different spring rates and ride heights and wider wheels.