HMRC Booklet 490 is an excellent guide, explaining the extended reliefs relating to travelling and associated expenses. It is available from the HMRC website (via the related links section of this page).
A supply teacher claimed a deduction for the cost of travelling between her home and the schools where she worked. Her claim was rejected and she appealed, contending that the expenses should be allowed, since she used her home for preparing lessons and marking work. The Special Commissioner rejected her appeal, accepting that she had a ‘second place of work’, because that the location was not a requirement of the job itself.[Warner v Prior, 2003 SSCD 109]
Tax will not be charged on the reimbursement to an employee, whose duties are carried on wholly abroad and who retains a home in the UK, of expenses, including hotel expenses necessarily incurred, in travelling, whether alone or with his wife and family to the country where his duties are performed and returning to the UK.
By concession, expenses of a spouse of a director or higher-paid employee who accompanies him on a business journey because his health is too precarious to travel alone are not assessable on the employee. (HMRC ESCA4).