There is a difference between "Historic" as a class, and "Vehicle of Historic Interest" with regard to whether an MOT is needed.
The reasoning seems to be connected with the 'suggestion' that so many vehicles of Historic classification are confusing the poor dears at MOT stations - there are so many items that are only relevant to more modern vehicles. I do not believe that an Historically classified vehicle AUTOMATICALLY becomes MOT exempt UNLESS it is declared so by the keeper when re-taxing.
Also - scroll down to item 6 under <b>Key Points</b> on this page:
What defines a "built up classic" - a Triton recently built from old engines and frames?
It's no wonder there is confusion.
Read the Government page: