whats the best way to turn 10 quid in to 20 quid?

Answer 1

It depends on more factors. If you have plenty of time, place it in the bank. At 7% interest, it will be 20 quid in 10 years.
If you need to make it fast, go to a casino and bet it all on "black" at the roulette wheel. Almost half of the time, you will walk away with 20 quid. The downside is less fun.