EIM32322 - Travel expenses: travel for necessary attendance: safeguards against abuse: journeys treated as private travel: example
An employee works in a dry cleaners in Carlisle. Her employer sends her to the Darlington branch to repair a machine that has been damaging clothes. While there she visits her ex- husband to discuss maintenance arrangements. She spends a longer time dealing with her private affairs than in fixing the machine.
Her main purpose in going to Darlington was to fix the machine. The discussion with her ex- husband was time consuming but was merely incidental to her business travel. So this is not substantially private travel, see EIM32320. She can deduct the cost of travel between her home and Darlington.