It should be about getting people from ICE to EV, no matter the cost of the car
I think that's a separate debate from the plug in grant. It needs a big stimulus, not a few hundred quid. PIG is the typical tailing-off grant that seeks to lessen the burden for early adopters and help manufacturing get to economy-of-scale with the aim that market price will then drive the purchase decision. Not long until EV is at parity with ICE, and for high mileage drivers it has been for some time.
When I bought my first EV the PIG was £5K iirc. It drops, the funds available are available to more people, the car price drops (my replacement EV was £20 cheaper, 3.5 years later ...). Those sorts of grants never actually cover the early adopters total additional cost ... e.g. original PV grants / FIT were much higher, but people who bought later got cheaper panels and ones that were better tech - more efficient, longer life.
I am disappointed that there is no incentive for the very high mileage drivers to buy (the more expensive) EVs. We have MS LR Raven because it does all the business journeys we make, whereas before we had to compromise and take the ICE for many of those. We have now replaced the ICE with an M3 as a consequence of buying the longer range MS. Can't argue with the one size fits all PIG though, much as I would might like some sort of sliding-scale that suited me, its complex and expensive to implement, and whereas an entrepreneurially driven outfit would find a way, Government doesn't have that same incentivised approach. Same as a 30 MPH rural speed limits at 2AM ...
Government seem hell bent on pump-priming EV through company cars. I haven't been able to think of a reason for that (my suspicion is that the "cost" actually circulates round as tax, eventually, if so it may well be cost-neutral). I'd be fine with giving everyone who wants an EV a £few-grand to encourage them (Norway have 0% VAT on EVs I think??) but that sort of stuff is often abused - the plug in hybrids that qualified for relief and the business drivers never bothered to plug them in.
Either way whoever you vote for the government always gets in ... and we are stuck with whatever they put in place