Note you have to be low risk to get it at £5 per month (i.e. non-smoker, etc). DO NOT LIE ON YOUR APPLICATION. If it doesn't work for you because you don't fall into the category, please move on as this deal is not for you.
£20 profit for those that get a £5 quote.
If you're feeling lucky, you could try cancelling after 3 months (£35 profit), but you're not guaranteed to get the giftcard at that point!
Credit to a1cat @ MSE.