You can use the Atkins shakes, ready to drink, very tasty.
Or, a bit cheaper and heavier on protein and vitamins/minerals, the EAS carb control shakes. £20 or so for 12, free postage, they come in chocolate or strawberry.
I get them from a site called Bodybuilding Supplements. Make sure you get the carb controlled ones. They also do a 20g carbs shake but I think it is for those wishing to bulk up! Ha not quite what we need...