"Whenever you move money around the world, banks take a cut, it's a big cut and it's unfair," says Kristo Käärmann, co-founder of TransferWise.

Together with fellow Estonian Taavet Hinrikus, he set up TransferWise, which aims to shake-up the banks' dominance of global money transfers and make it cheaper for people to move money overseas.

Four years on the business transfers £500m ($760m) monthly.

The firm's co-founders explain how they got started.