Bank it and don't spend any of it for at least 3 months to ensure it is real.
If after this time it clears and is accessable then move it to a saving account and leave it for a further 6 months at least.
Least if it is fake you will be able to pay it back and keep any interest earned
IGNORE EVERYTHING I HAVE JUST WRITTEN.
This is a total scam.
DON'T bank the cheque at all !!!
This is basically money laundering with fraudulantly acquired cheques.
I bet the instructions go something like this.
1/ Bank enclosed cheque and send money to some dodgey address.
2/Once received the "Prize" will be released to you.
Yeah right !