CMS Electric Vehicle BIK or P11D

Pilgrim007

My company is currently providing me with a van for which I pay the fixed fee BIK as part of my tax and CMS payment.
Due to the ethical credentials and other reasons they now wish to change this next tax year to a full electric car BEV.
Therefore, I am concerned that this will increase my monthly CMS payments as it will be effected by company car tax? I cannot see anywhere if the CMS use either the P11D value of the car or the BIK value when making their annual child maintenance  calculations.
If it’s the BIK value then I am told that it will be the car value for example £35,000 then I will pay 2% of this value;  £700 per annum as a 20% tax payer? Please can anyone advise if this is correct? 

What I do not want is that the actual car value, which is a higher P11D value is used for their calculations or ideally a value higher than I am already paying for my van.
Any help and advise appreciated.