By simply betting on red or black at Roulette for example, starting with £1 and putting your entire winnings back on each time 21 straight wins would net you over a million at odds of just over 1 in 2 million (compared to 1 in 14 million for Lotto).
I know it's still 1 in 2 million, but the thought of turning a quid into over a million in just 21 spins in very tempting
