The general rule for employees: expenses: deductions not to exceed earnings: example
An individual is employed as a teacher and separately employed as coach to a local youth football team. As coach she is paid £100 a year but she incurs expenses of £1,000 a year in travelling to away matches. She pays the expenses herself and is not reimbursed by her employer.
She is only allowed a deduction of £100 for her travelling expenses. She cannot claim a loss for the remaining £900 and nor can she deduct that amount from her teaching income.