Does an employee continue to accrue annual leave if they fall ill or are asked to stand down?

UK law entitles all full time employees to 5.6 paid weeks, or 28 days, of annual leave (which can be inclusive of bank holidays). The entitlement can vary in terms of hours/days worked or any additional contractual agreements.

On the face of the WTR (Working Time Regulations Act) 1998, it appears that this leave accrues during a sabbatical, which would also apply if you were to stand down at work but remain employed. 

So, as long as the individual remains a worker, then their holidays will accrue.

This is why set holidays are so important and flexible leave is discouraged.