Travel expenses: general: introduction: expenses do not have to be wholly and exclusively incurred: example
An employee has to travel to New York on business for two weeks. While she is there she has a free weekend and spends it taking a break in Boston. The cost of her flight to New York and any other necessary travelling expenses are deductible. They have been necessarily incurred in travelling to a temporary workplace. The fact that the break in Boston means that the travelling expenses have not been incurred wholly and exclusively for business does not matter.
The costs of the break in Boston, such as travelling to Boston from New York and the cost of staying in Boston, are not deductible. These expenses are not attributable to attendance at the temporary workplace.
You can find detailed instructions about the expenses incurred in attending overseas conferences, seminars or study tours at EIM31950.