The national lottery has an expected return of roughly 50% of your bet. They give about 30% of your bet to charity. So if you gamble £100, you'll end up with £50 in your pocket and £30 donated to charity.

Blackjack on the other hand returns roughly 90% of your bets over time if you play well. So if you donate £40 to charity and take the remaining £60 to a blackjack table you'll end up with more money going to charity and with more money in your pocket.