The voucher is only valid for a specific amount. So, if your BA Holiday hotel was £1,000, then the card given to the hotel would be loaded with £1,000. The same with the car rental companies, or any other extras you bought. BA Holidays would essentially give them a virtual prepaid credit card, with a specific amount. The hotel can charge less than the amount on the card, but not more. That £1,000 bar bill would not have gone through on the card.