NIM06310 | Class 1 NICs: Expenses and allowances: Travelling expenses: Depots and similar bases
From HM Revenue & Customs · National Insurance Manual
General
Where an employee regularly attends a workplace because it is the base from which they work or it is the place where they are routinely allocated tasks, attendance will not be accepted as for a limited duration or for a temporary purpose.
Not all places from which an employee works or at which they are allocated tasks is necessarily a permanent workplace.
A depot or similar workplace will be regarded as a permanent workplace if
the employee attends it regularly, and
the main reason the employee goes there is because it is the place from which they work or at which they are regularly allocated tasks, and
it is the main or only place from which the employee works or at which they are regularly allocated tasks.
If an employee regularly attends a workplace to be routinely allocated tasks the workplace will be a permanent workplace even if certain tasks are allocated to the employee elsewhere.
See EIM32160 for further guidance on this.