That's right, you'd get a voucher which would be worth £15 in store for general shopping, £30 if you doubled up in storefor things like wine and clothes (can't remember exactly what things they let you double up on, it'll say on the website), and £60 if you converted it to dels.
However, I've always found car dealers won't let you put it all on credit card, last time we could put a grand on, but the rest had to be debit card.