I have a leased car through a salary sacrifice agreement. I wanted to change to an electric car. But my employer says it can only be done on exceptional circumstances, as HMRC is strict on this.

If you look at HMRC’s Employment Income manual (here), you can see that it states: 'Where an employee chooses a benefit instead of some form of cash pay, the value of the benefit treated as earnings from the employment is the greater of the amount of cash pay given up and the taxable value of the benefit under the normal benefit-in-kind rules'. However, if you look at EIM44060 it states: 'The optional remuneration arrangement rules do not apply to cars with CO2 emissions of 75 grams or less per kilometre. Cars with CO2 emissions of 75 grams or less per kilometre continue to be taxed on the cash equivalent of the benefit without having to make a comparison with the salary foregone'.