NIM01181 - Class 1 Structural Overview from 6 April 2003: Changes to the deferment process from 6 April 2003: Unofficial Deferment
Some employees defer payment of their Class 1 NICs in some of their employments without authority from HMRC. This is commonly referred to as unofficial deferment.
Employers who continue to operate unofficial deferment must obtain from their employees a deferment certificate. Any underpayment arising because of unofficial deferment remains the responsibility of the employer.