Lorz: if you are a professional witness, doctor, engineer, etc, then there is a recognised scale of fees payable, depending on whether you were there for a full day, a half day, a consultation or just on standby. If you are not, then your reasonable expenses for the day should be submitted. Its not a money making racket, its to compensate you for your expenses.
Rizoff: You should claim your expenses from who ever sent you the summons. The exception I would see would be if you were the Defendant, that is the person sued. If you were, then your insurance company dealt with the claim on the basis that you would be present. You should write to the solicitor who sent the summons, set out your expenses, explain you don't have receipts, and they should be paid. I'm assuming your expenses are something like meals/parking as loss of earnings should be substantiated by your employer.