Any change could also be something to do with parts of the Immigration Acts 2014 and 2016. It's something like: under the 2014 Act a UK driving licence is revoked if they do not have lawful status; under the 2016 Act it's a criminal offence to drive in the UK if you do not have lawful status and is up to 12 months in jail.
Those two Acts were brought in to stop the abuse and also to end the making it so easy for illegals to live in the UK. Perhaps the wait to take a driving test, is to stop those who visit or who are on a short term visa, but who planned to overstay? Illegals often get jobs as drivers. Those lawfully in the UK can use their own country's driving licence for up to 12 months.