Are you getting witness expenses? Usually these would include loss of earnings where you take a day off and don't get paid; thus retaining your holiday entitlement and not losing any pay. You should check this with the solicitor that issued the summons. Payment of these might take a while as they form part of the legal costs for the side that is calling you to witness. It's a while since I did stuff like this but it is not up to your employer to cover the day.