Instructions:It did say it was for first time customers only but just worked for me :) If it doesn't work on current account, maybe start a new one with a different email address.
Only 1 use per customer. Valid on grocery orders checked-out before 10pm on 18th January 2010. If order is amended after this date the discount will not be applied. Only valid to customers who registered on the groceries site after 17th December 2009