How? Quite simple. Move a load of money into Euros, dollars and yen before a referendum.
If it goes one way, you won't lose much. If it goes the other, the £ will fall dramatically, which means in dollar and euro terms things like house prices in the UK will fall.
Then it's just a matter of when to use your foreign funds to buy up the country on the cheap.
If you're asking the question now, it's too late.