The upside: Winnings are tax-free. Capital gains tax (CGT) of 20 per cent of the gains is not payable, as it would be if investors buy and sell shares.

There are no commissions or other fees. The only charge is the spread, which is the difference between the buy and the sell price.

For example, the buy price for Bank of Ireland might be €11.60, but the sell price could be just €11.45.

Unlike most retail investments through a stockbroker, investors can bet on markets going down as well as up.

The flipside: Losses are not tax-allowable. This could be important, as investors can offset gains made on investments with losses made on others, reducing their CGT bill.

A deposit will be required for each bet, with the exact amount varying according to what is known as the initial margin requirement.

The company may make a "margin call" if the deposit has been lost and you fail to make further payments on request. This could crystallise heavy losses, barring the chance of a recovery.