The general rule for employees: expenses: necessarily incurred: example
An employee who is a sales manager is asked by her employer to attend a dinner dance for sales staff. She has 2 small children and needs to pay a babysitter to look after them while she is out. She asks for a deduction for the expense of the babysitter.
No deduction is due. The expense is not one that is necessarily incurred in carrying out the duties of her employment, see EIM31645. Attending the evening function is not part of the duties of her employment as a sales manager even though her employer has asked her to attend. Nor is the expense one that each and every employee in her employment would have to meet; not all employees would have children.