Up to twenty per cent of new cars on the UK's roads could still be petrol and diesel models in 2030 after the government published guidelines for phasing out new internal combustion engine cars and vans by its new extended deadline of 2035.
Under the terms of the so-called zero-emissions mandate published by the Department for Transport, 22% of new cars will have to be zero-emission from January next year.
The UK Prime Minister announced a five-year delay to the ban on new petrol and diesel cars and vans earlier this month, calling it a "pragmatic" approach to achieving the UK's net zero goals.
The mandate has been anticipated by the industry for 2 years, with some manufacturers privately frustrated that it has only been published three months before it applies.
If companies exceed the mandate levels they can bank, trade or sell their allowance, while those that miss the targets can buy allowances to offset fines.
Even after 2035, there will be no outright ban on owning a petrol or diesel car and there are likely to be millions still on the road for years afterwards.
The car industry still faces uncertainty over EU rules due to apply next year governing how much of a vehicle has to be produced in Europe or the UK to avoid 10% tariffs.
The "rules of origin" require 45% of a vehicle's total value must be derived from home-produced components from 1 January, a target that is harder to achieve for electric vehicles because the battery comprises so much of the value.
Most manufacturers in the UK and EU rely on batteries produced in Asia, putting the entire European industry under pressure. The UK is pushing for a relaxation of the rules, with backing from Germany.
Mike Hawes, chief executive of industry group the Society of Motor Manufacturers and Traders, said: "The automotive industry is investing billions in decarbonisation and recognises the importance of the zero-emission vehicle mandate as the single most important measure to deliver net zero.
"We welcome the clarity the mandate's publication provides for the next 6 years and the flexibilities it contains to support pragmatic, equitable delivery across this diverse sector."
Ford, which was highly critical of the delay to 2035, saying it undermined confidence in British industry, welcomed the mandate, which it said it had helped inform.
"Alongside the SMMT, Ford has provided input to the Department for Transport to help shape the mandate in the early years and it is very welcome to see some of those ideas reflected.
Transport Secretary Mark Harper said: "The path to zero-emission vehicles announced today makes sure the route to get there is proportionate, pragmatic and realistic for families.
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