EIM36510 - Deductions from earnings: capital allowances: expenditure on small items of plant and machinery
It can be impractical to apply the capital allowance regime in relation to insubstantial expenditure on things like tools or small items of office equipment such as cheap pocket calculators or staplers.
There is no objection, therefore, to giving deductions for such items under section 336 ITEPA 2003 if they have been necessarily provided by the employee solely in performing the duties of the employment.
As regards claims for the cost of books, see EIM36710.