BEVs to be exempt from London Congestion Charge until 2025 (PHEVs until 2021)
From April 2019 on, only plug-in electric cars will be exempt from London Congestion Charge, as British capital is trying to lower emissions. The upcoming changes will require Private Hire Vehicles (PHVs), like Uber and Addison Lee, to pay £11.50 ($14.5) a day. It's expected that in result, 8,000 fewer of those will be driving in the city center.
"Zero-emission-capable" vehicles (aka plug-ins and maybe hydrogen fuel cell cars) will be exempt until 2021. After then, only pure electric vehicles will be exempt from the London Congestion Charge, and it will also not last forever, as the deadline is 2025.
If we understand correctly the intentions of the authorities, from 2025 there will be no exemptions and only zero-emission vehicles will be granted access (maybe beside privileged vehicles).
That, combined with new electric buses and a requirement for zero-emission-capable taxis, should help to clean the air.