If you are not registered for V.A.T., you should not charge V.A.T. on your sales and cannot claim any V.A.T. on your purchases and expenses.
In Parameters > General > V.A.T. Reporting Periods, you should leave the period fields blank as your business will not be required to produce V.A.T. returns. and in V.A.T. Rates & Default V.A.T. Codes, set the Default V.A.T. code to N for Sales Ledger, Purchase Ledger and Cash Book.
Process all your transactions with V.A.T. code N and don’t enter any V.A.T. amounts for expenses & invoices from your suppliers and don’t charge V.A.T. on your invoices to your customers.
If you have any doubt, you should consult your bookkeeper, accountant or your Prelude distributor.