I am of the view the government should not be making any grants because it reduces the motor industries' motivation to get the price down.
The strategy appears to have been to load EV's with unneeded accessories, presumably, they think this will make the car more attractive, and also they are cashing in on the green market, "if it's green we can charge more."
As I see it, the electric motor and its reduction gear lend themselves to full automation, and have fewer components relative to an IC engine.
The chassis and running gear have to carry more weight continuously, and of course the present batteries are expensive (though there are other batteries waiting for investment that should be lighter and cheaper) The electronics, whilst expensive to develop are cheap to produce and again can be automated.
From the governments point of view, there is a need world wide to reduce green house emissions, some of which are short term projects some will take a much longer time scale.
ICE cars have a relatively short life cycle whereas ships and power stations have a much longer life cycle, so pushing changing from ICE to EV gives a quick return.
With EV's the governments dilemma is to balance keeping the changeover progressing and keeping employment in the car industry high but as pointed out by Drivingforfun the discount is not enough to send people rushing to the showrooms.
On top of that, world markets are in chaos due to wars and the Trump effect, so people are not in the mood to splash the cash.
Overall then, I would not subsidise, leave the fixed cut off date for ICE vehicles, and if help is felt to be necessary, put money into manufacturing alternative batteries and Hydrogen in the UK.
