P11 D form

Hi everyone I work in NHS and my trust offer salary sacrifice scheme for hospital parking. There is a fixed deduction every month for parking before tax. Trust has never sent P11D form for this in the past, however this year they have sent P11D mentioning this benefit. In my understanding I will have to add this benefit now in my self assessment which in the final calculation of tax is added to the income and hence I am liable to pay tax for this benefit. I just want to understand this process that if the trust is deducting the amount for parking before tax every month to give employee a benefit to save tax, then why in the end of the year by declaring this amount we end up in paying tax? This also would be an issue for people who have bought lease car as salary sacrifice scheme. It seems every month we are saving tax by salary sacrifice but then in the end of the year we end up in paying tax. Am I understanding this correctly or am I missing something here? Thanks in advance 

Name removed admin .

Hi AshT
We would direct you to read the current guidance here:
Expenses and benefits: car parking charges
Please ask your employer for an explanation why payment is being deducted through payroll and a P11D is being submitted.
Depending on answer you receive from your employer we would suggest you contact the Self Assessment helpline.
Self Assessment: general enquiries
We Can also advise that P11D details should always be entered on Self Assessment Return.
Thank you