If you, as an employer, provide any benefit to an employee, you are required to complete a form P11D and submit it to HMRC. This form records the cash equivalent of each benefit provided during the tax year. So, if you provide medical cover, gym membership, a car, fuel etc. then you will need to make a submission.
The deadline for this to reach HMRC is 6 July, and penalties will start accruing for any returns not submitted by 19 July.
Some of these benefits provided will result in a Class 1A national insurance charge, payable by the employer. Payment of this is due by 19th July (or 22nd if payment is made electronically).