He needs to make sure his contract states that his home address is his main place of work, then any business travel is just that business travel so he should be able to claim expenses for each journey
HMRC advises
Business travel and private use
11.25 'Business travel' means travel for which expenses would qualify for deduction if they were incurred
by the employee. Broadly, this means travelling expenses which involve two types of business
journey:
• journeys which employees have to make in the performance of their duties, and
• journeys which employees make, to or from a place they have to attend, in the performance
of their duties - but not journeys which are ordinary commuting or private travel.
Detailed guidance on the types of journey which give rise to qualifying travelling expenses is
contained in booklet 490 Employee travel - A tax and NICs guide for employers.
Section 118(2) 11.26 'Private use' means any use other than for the employee’s business travel. This therefore includes
commuting journeys.
Companies do have their own policies though so he needs to check with them and ask for a copy of the fleet policy and the expenses and benefit policy
this is a link to the HRMC expenses
http://www.hmrc.gov.uk/guidance/480.pdf
This is our co policy
Business mileage is defined as the distance travelled from the normal place of employment (e.g. the office) to the business destination. If the journey starts/finishes at a different location (e.g. home) then it will be the lesser of:
a) the distance actually travelled
and
b) the distance that would have been travelled had the journey started or ended at the normal place of work