In 2018, a trend in car ownership outside of any defined recession was noted (a 5% drop)
https://assets.publishing.service.g.../800502/vehicle-licensing-statistics-2018.pdf
Where does that stat come from? The source you've provided a link for shows (page1) a 5% drop in
first-time registrations of
vehicles but that isn't the same as 'car ownership' because (a) it doesn't take into account the scrappage rate and (b) includes all motorised road vehicles subject to the registration system.
Figure 1 shows the breakdown by vehicle type. There we can see first-time registration of
cars fell by 6.7%, but all categories other than 'motorcycles' also dropped, the highest fall being buses and coaches at -8.8%. This demonstrates the factors involved are far more complex than young people's interest in climate change. (the growth in motorcycle sales is notable).
Total licensed vehicles (page 7) is really what we need to be looking at. This shows us that in fact the total number of licensed cars (in GB)
increased by 1% in 2018. The bottom of page 8 gives us the clue that this is partly explained by an increase in average age of vehicles: indicative that people are keeping their cars longer and hence reducing the number of first-time registrations.
...thought by some to be caused by lessening interest in cars from young persons, (maybe in consideration of energy use and climate change).
That is speculation though, and since the premise (car ownership dropped) is incorrect we should probably look elsewhere for some answers.
My thoughts are that an increase in costs (partly exchange-rate driven) will be a factor, as well as a change in people's spending behaviour with one eye on Brexit. Delaying the purchase of a new vehicle is a simple and effective strategy for people and businesses who wanted to limit their spending in the run up to Brexit.
Another reasonable speculation would be that Government announcements regarding future bans on ICE cars, and also the EV market starting to take off, may lead to some people delaying the purchase of a new vehicle in order to see what happens. The attack on Diesel cars will also make people nervous about committing significant personal resources to any particular fuel technology now, when the vehicle may become virtually worthless in short order.
Meanwhile, rail travel has continued it's climb.
Here we need to note that whilst the data for cars was about vehicle
ownership, the data for rail travel relates to
passengers and/or passenger km. Rail passenger numbers and passenger km is relatively easy to quantify, and a robust system is in place to monitor the figures.
Car driver/passenger figures are harder to work out and rely on estimates using sampling techniques. (e.g. Household survey data) The accuracy of the data therefore depends on the robustness of the methodology and the assumptions made in the sampling process. Subtle changes in usage may be missed because the methodology cannot detect them.
In the next 10 years there will be even more downward pressure on car driving as environmental measures and restriction start to bite...
That relies on an assumption that additional environmental measures and restrictions will be applied, and that they will take effect in the next 10 years. I would suggest it is unlikely to happen in the first 4 at least, and quite possibly the next 9.
Any measures and restrictions applied will initially target the most polluting vehicles. It will be difficult to restrict use of EVs (on pollution grounds) - not least while their purchase and use is incentivised to hasten the change away from ICE vehicles.
And then when a majority of cars are EV, the
environmental case for restricting car use (in favour of rail) becomes far weaker. Congestion is a different issue - and for that it is worth again noting the increase in first-time registrations of motorcycles.
...so it is not unreasonable to expect both of those trends to continue and plan accordingly.
Broadly that approach is familiar to us as 'predict and provide'. In the case of strategic road building it was largely discredited in the 1990's on the basis that providing more will stimulate demand, with the increased demand in turn resulting in increased predictions and further capacity requirement.
I've not yet seen a cogent argument as to why a methodology which has been rejected as flawed when it comes to road building is still seen as wholly valid when it comes to railway building. (or for that matter airport runway provision and house building)