"High Court Judges Said [the UK] Was Failing to Meet EU Pollution Limits"

From the BBC:
New diesel and petrol cars and vans will be banned in the UK from 2040 in a bid to tackle air pollution, the government has announced.
Ministers have also unveiled a £255m fund to help councils tackle emissions, including the potential for charging zones for the dirtiest vehicles... The timetable for councils to come up with initial plans has been cut from 18 months to eight, with the Department for Environment, Farming and Rural Affairs (Defra) wanting to "inject additional urgency" into the process.
It follows the government being given its own deadline of 31 July after High Court judges said it was failing to meet EU pollution limits.
I thought we are on the way out of the EU, so why did they even take that into consideration?
Also, the government can get away with persecuting smokers because non-smokers are in a significant majority, but the fact is, most households own at least one car; those who don't probably take the bus; and surely everybody buys stuff in shops that was delivered by diesel-powered lorries.