We cannot advise you on policies you have with your employees.
We only advise on what is covered by an exemption and benchmark scale rates where they apply.
Guidance on when travel qualifies for tax relief is found here -
When travel qualifies for tax relief (490: Chapter 2)
As you will see, this does not make stipulations such as the one you suggest.
Guidance on employees who work from home is found here -
Employees who work at home
Again, there is not stipulations such as you suggest making to your employees.