VQOTW: CHANGE IN POLICY FOR RETAINED DEPOSITS

My client and her husband run a boutique hotel in partnership. Due to the location and quirky nature of the décor, they are increasingly getting requests to host celebrations and parties in addition to overnight accommodation. As the financial outlay in preparing and staging the events can be quite considerable, the client asks for a 25% deposit up-front, which is non-refundable if the event is cancelled. Please, could you advise on the VAT treatment and time of supply implications of these deposit payments?