With that mileage and purely a financial decision- there’s no other option than electric. If you take the grant and get the 5008 – you’d be, conservatively, £10k worse off over a 3 year lease period. I see the following options:-
1- come off the scheme and enforce the subsidised transport.
2 – get the 5008 electric without the grant. The grants team will not let you top-up under any circumstances.
3 – use the grant towards a 5 seater. Will be £5000 better off than option 2 with 2 fewer seats! – this is only if grants team agree to this (you may have only been offered a grant based on the need for a 7-seater)
I believe that the policy is all wrong in this circumstance- the fuel type in this case is a need rather than a want.
Good luck