A form P11D should be completed by employers when employees or directors are in receipt of shares, or share options are exercised and there is income tax liability.
As the valuation of share related benefits is not always able to be completed quickly there is no statutory obligation on employers to value the benefit that the employee receives. An estimate of the value may be needed in order to operate PAYE, but that is not a value which is necessarily correct for assessment (SA) purposes.
In addition employers have comprehensive responsibilities to return details of share related benefits. See SSM9.3. Employers will usually provide a valuation of shares, which the employee will usually accept. The employee may however if he wishes provide his own valuation, which would then need to be checked with Shares Valuation Division. SSM7.1.
The employer therefore does not have to enter a value of share related benefits on the P11D, but instead completes Box N with a tick if there are such benefits in the year.