The government has decided that most vehicles first registered over 40 years ago, on a rolling age basis, will as of 20 May 2018 be exempt from MoT testing, unless they have been substantially changed.
PSVs with 12 or more seats and large goods vehicles (i.e. GVW over 3.5 tonnes) will not be subject to a general exemption from testing at 40 years.
Details at https://www.gov.uk/government/consultations/roadworthiness-testing-for-vehicles-of-historic-interest
