Your contract of employment may contain written terms specifying what expenses are to be reimbursed and in what circumstances, for example:
travelling expenses to a location other than the normal place of work;
hotel accommodation when staying away from home for work;
mileage expenses for use of a private car when travelling on company business;
petty expenses for materials necessarily purchased for the purpose of carrying out duties; and
relocation expenses on transferring employment to a new location.
It is essential that you get receipts for reimbursable expenses. Most employers will have an expenses policy, with rules and procedures for claiming expenses.
Some expenses paid by the employer may be taxable.
It is very important to follow any expenses policy carefully and to the letter, as any breach can have serious disciplinary consequences, including dismissal, with or without notice.