slatternly - with you. I thought you were angling for a get out clause to be able to do it once a week! 
Absolutely you can have the odd cheat here and there. It's called 'having a life'! The great beauty about low carbing, once you have become ketogenically-adapted, i.e. you are fat-burning rather than carb-burning, you can do this without too much damage.
If you can, though, look for low carb alternatives, to minimise the damage - so if you can substitute salted nuts for crisps, that would be better.
And just keep an eye on it, so that it's not happening too frequently, otherwise you will fritter away your hard-won weight loss.
I started low carbing properly/seriously this time last year, and it took me until December to lose two stones. During the year, I continued to drink alcohol at the weekends - sometimes rum and soda but most often lots of white wine. I've also been for dinner with other people where I have been served really carb meals. I've been out for dinner at restaurants where it's been difficult to avoid the carbs. I went on holiday for two weeks where I was completely off piste, and had two weekends away with DH and a business trip to Athens where I was not exactly 100% low carbing. Every Friday, DH and I have an Indian takeaway. Usually I have tandoori/tikka meats with low carb veg as a side dish - but not always. I can happily do without the rice, but have been known to tear off a corner of naan bread.
My point being that eating this way has allowed me to feel I'm leading a 'normal' life; I have never felt deprived. However, I have had to accept the inevitable consequence in that it took me a very long time to lose the weight - and I still have at least another half stone to go - if you add the weight put on over Christmas, probably 10lbs to go. If I'd been completely 100% Bootcamp, I could have lost that weight by the end of May/early June.
Choice is up to you!
The key thing is making sure that you are committed to low carbing as a WOE and that you can easily get back on the wagon after falling off it - either intentionally or accidentally.