It is very simple, Camelot issue packs of scratch cards for different demoninations, starting at £1 and going up to the £10 card. A fixed percentage of the pack have to be winners and a fixed percentage of the game have to be the jackpot amount, they issue hundreds of packs of each game, there does not have to be a jackpot prize in each pack, only the percentage of winning cards, which means every winning card in a particular pack may just be a £1 prize or face value prize. The game overall has a closure date, and if all the jackpots have not been won close to the closure date, Camelot advertise the fact. This is public information but it does not necessarily mean the jackpots will be won, anyone one armed with the information about a game due to close with unclaimed jackpots would have to locate every pack still on sale in every outlet and buy every remaining unsold ticket, impossible to do.