Hey Twiowl - yep they're allowed There's a thread on this somewhere here that you may find interesting. I contacted SnS about it and they basically said one pack a day (ca. 200g) is allowed. However, as Weasey says there prob isn't a limit since there is nothing in them but water and soluble fibre! I do limit them to one a day though and I have used them from the very first day on SnS and they are a lifesaver! They make the packs into a real meal - I have got the pasta, noodle and rice ones and all are nice enough!
Have been looking into this myself today! They sell them on amazon - varoious amounts and prices.they also do a range at holland and barratt health shop. Can't wait to try them!