Of course.

You could also seek some kind of TOIL arrangement, by which the time is worked back, or have them take it from their allowance of paid holiday, or have it as statutory carer's leave (which is also unpaid). Any of those are reasonable approaches to the scenario, assuming you are willing to relinquish their labour in the interests of a happy employee.

www.gov.uk/carers-leave

In reply to Robey:

Thanks for this, really appreciate it.

It all depends on the company really. Whats right in one company is not necessarily right in another.

I'm not sure I'd go to HR to ask this anyway- I'd go to my line-manager. And as a line-manager I can't see why I'd refuse it or tell someone it would not be paid. That said, I'd be aware incase it was going to become a regular issue.

I assume yours is a rather large company given you state that an employee is "requesting", to leave early? I'd be most interested in why HR is involved.