Gamestation changed its terms and conditions to say that anyone buying goods from it online on 1st April this year and not clicking on a link contained within them would forfeit their soul.

The prank, which was designed to highlight that terms and conditions are almost never read, fooled all 7,500 customers who made a purchase that day, a company spokesman said.

The new conditions said: "By placing an order via this web site on the first day of the fourth month of the year 2010 Anno Domini, you agree to grant Us a non transferable option to claim, for now and for ever more, your immortal soul".

"Should We wish to exercise this option, you agree to surrender your immortal soul, and any claim you may have on it, within 5 (five) working days of receiving written notification from gamesation.co.uk or one of its duly authorised minions. We reserve the right to serve such notice in 6 (six) foot high letters of fire, however we can accept no liability for any loss or damage caused by such an act," said the terms. "If you a) do not believe you have an immortal soul, b) have already given it to another party, or c) do not wish to grant Us such a license, please click the link below to nullify this sub-clause and proceed with your transaction."

That link led the user to a page saying that the clause was an April Fool, congratulating the user of being "so vigilant" and offering them a £5 voucher.

Gamestation said that 7,500 people made online purchases on 1 April and that none of them clicked on the link, meaning that all the customers failed to check the terms and conditions closely.

The retailer carried out the experiment because it had previously conducted research which indicated that as few as 12% of customers read terms and conditions when buying online. In fact its experiment showed that the situation is even worse than it had thought.

Gamestation said that the prank was designed to remind customers that when it came to buying online "the devil is in the detail and ... always read the terms and conditions", according to a company statement.

The results of the experiment chime with others' findings. Computer optimisation software maker PC Pitstop tried a similar experiment. It buried a clause in its end user licence agreement (EULA) offering money to anybody who read the clause and sent an email to the address within it.

It said that it was only after four months and 3,000 downloads of its software that somebody finally emailed the address and claimed a $1,000 reward.