"Each code can only be used once. A code can only be gained from purchase - the mail does not lose out on revenue and there is no doubling up of codes."
Ed - I do understand that, but if the Mail has budgeted for example for 30% of purchasers to join the scheme, they will be prepared to pay out x amount of rewards. But if the people who buy the paper but are disinterested in the scheme pass on the numbers, so that non-purchasers can benefit, the amount of rewards they will pay out increases and the sales of papers does not. This could cause them to cancel the scheme.
But as well as that I am generally in favour of obeying the rules, so I think that numbers should only be used by the people who have purchased the paper.