From TFL website:
Requirements for taxi and private hire vehicles (PHVs) are as follows:
From 1 January 2018, new diesel taxis will no longer be licensed in London
From 1 January 2018, all taxis presented for licensing for the first time will need to be zero emission capable; emit up to 50g/km CO2 with a minimum 30 mile zero emission range. A zero emission capable taxi must be petrol if an internal combustion engine is used
TfL will provide grants of £3,000, on top of the Office for Low Emission Vehicle’s plug-in car grant, towards the purchase of a zero emission capable taxi from mid-2017 to 2020
TfL will introduce a voluntary decommissioning scheme from mid-2017 until 2020 to remove the oldest taxis from the fleet. Owners of taxis over 10 years old will be able to claim a payment of up to £5,000, depending on the age of the vehicle, from TfL by forfeiting the ability for that vehicle to be relicensed as a taxi in London
From 1 January 2018, all vehicles licensed for the first time as PHVs must be Euro 6, unless petrol hybrid when the minimum standard is Euro 4
From 1 January 2020, new vehicles (those up to 18 months old) licensed for the first time as a PHV must meet the approved zero emission capable requirements. Used vehicles (those over 18 months old) licensed for the first time as a PHV must be Euro 6
From 1 January 2023, all vehicles licensed for the first time as PHVs must be zero emission capable
For PHVs, any vehicle meeting the eligibility criteria for the Office for Low Emission Vehicles’ plug-in car grant will be meet TfL’s zero emission capable requirements. An eligible vehicle will emit either up to 50 g/km of CO2 with a minimum zero emission range of 10 miles, or up to 75 g/km of CO2 with a minimum 20 mile zero emission range
TfL is working with suppliers to deliver 150 rapid charge points by 2018 and 300 by 2020 to support the electrification of taxis, PHVs and other commercial fleets
Three manufacturers are developing zero emission capable taxis, with the first vehicles expected to be available for purchase in mid-2017
I am not sure of the lifetime of a London Black Cab, but from some of their appearance it seems like a very long time. I imagine that the Mayor of London would have to be confident in his ability of re-election without any London black cab votes if he plans on making the necessary legislation to get the huge number of highly polluting vehicles of London’s roads. The current legislation, referenced above, do not go far enough.