Balancing the books on missing tax revenue.
In 2018/19 HMRC collected £1.59bn in BIK (an increase of £40m) and £660m in NICs (£30m more), despite HMRC reporting 50,000 fewer cars (at 890,000).
They also collected £27.99bn from fuel duty.
So thats £30bn which is going to reduce year on year. Unless you think the government are going to replace that £30bn by taxing people more, I would expect BIK to continue at 1% increase each year for the short term but then to increase in bigger jumps until 2030 and they will aim for parity.
How they propose to replace the £28bn from fuel duty is a trickier problem. Perhaps a "surcharge" on chargers kw once there are a lot more chargers and a lot more BEV in the country.
ANybody who thinks BEVs wont get taxed like ICE cars have are kidding themselves. I know the gOvt have always claimed that duty was there for environmental reasons but its always just being a money raising tax IMO.
Same with BIK. They may well have tagged it onto co2 from the car but how you can have somebody being supplied a £130k Taycan which might be costing the company £1300 per month on lease and there be zero benefit in kind to the employee shows its nothing more than a subsidy to get people swapping over from ICE cars now.