Instructions:Enter the code GIFT100 at checkout to get £100 off when you spend £250.
Thanks to beccagrace over on MSE for spotting this.
Edit: For the code to work every item in your basket must be over £100. So order a £150 item and a £100 item and it works. But if something is under £100 it only deducts a smaller amount (ie if you have a £50 item in your basket and a £200 item the code only deducts £50).