This will depend on the deal that you are looking at.
For Land Only Holiday Deals, you only need to purchase 1 x voucher for the number of rooms you require.
For Holiday deals that include flights, you must purchase 1 x voucher per person
For group tour deals, you must also purchase 1 x voucher per person
If you are traveling on your own, please check the Fine Print whether a Single Supplement surcharge is applicable to the deal you are interested in