I've done Atkins to great success over the years, but I tend to do it without shakes, fake foods, or trying to replicate high carb foods too much (at least unnaturally). I focus more on whole foods. Read the book, even if you've read it before.
Regular whipped cream is naturally low carb. You can add Splenda or other AS (Truvia and the other stevia based mixed AS is supposed to be available in the UK this month). Sometimes you don't need sweetener if you're on the rung which allows berries. Sometimes your palette adjusts to less sweetness and the berries are enough without added AS.
Here are some suggestions for foods:
Black Farmer sausages. Really, the sausages here can be pretty carby. BF are low carb and gluten free. There are a few others, but you need to keep an eye on the carb levels.
Riverford does a "seasons" veg box which is potato-free. It does have carrots though, but they are added pretty soon after induction, so...They also do a pretty good salad box.
Most of the shops sell salted macadamia nuts. Costco sometimes has them in bulk. Costco also sometimes has wasabi almonds.
Most sugar-free squash is around 1 carb a serving, properly diluted. It's pretty good in fizzy mineral water.
They sell sugar-free jello.
Egg-white and AS meringue deserts are pretty simple.
Once you can eat fruit, eat it. If it's not in season, buy frozen. Again, Costco sells big huge bags of frozen berries.
With a little work, celariac sliced up and fried on a moderately low heat with a good slug of oil will make the best chips. Better than regular in fact.
Focus on the basics. Veg, eggs, meat, and moderate dairy. IMO, if you have to have a sweet treat, having something like a Pepsi Max is a lot better than getting into the trap of buying sugar-free chocolates where portion control and problems with sugar alcohols have be dealt with.
Really consider doing the no-caffeine thing if you drink coffee. It really helps me, but then I always break down a few weeks in and get a coffee.
This site is for a UK based diet loosely based on Atkins and other low carb plans. While you should try to stick to Atkins if you're doing Atkins, their recipes are UK based and tend to be awesome:
http://www.pig2twig.co.uk/Good luck.