For Collect Only Items, select 'no postage' in shopping basket
Under your address, select the choice 'I want to pay a CDI invoice' as the posting State/county. and then select 'No postage charge' in the postage class on the next page of the checkout. This way you not get charged postage, as you will be collecting.
(If you dont understand these instructions, don't worry we will manually adjust the payment amount accordingly at our end before the payment is processed.) (We can do this easily as all payments are only pre-authorised until despatch.)