I got stuck at that same point - ie after around 2.5 stone (around 9 12, down from 12 5) but with 7lbs to go (original target was 9 5). Was doing tesco diets, which is like weightwatchers.
I tried dukan - lost 5lbs the first attack week, but then decided that the protein only days were not for me (various reasons including I don't think its healthy plus I got v constipated), especially as by that point I had so little too loose. Atkins didn't appeal because I couldn't bear to eat the fat!
So I did dukan BUT did protein and veggies every day - I have ended up being 10lbs under my original target as weight came off so easily!!! Back to 1-2lbs a week once I moved onto dukan! I plateaued again at 8 10 but that's because I am thin enough! I Have now maintained easily that for a couple of months using the dukan consolidation plan, but I still rarely do a protein only day.
BTW before my pregnancy and diet normal good weight was 9 5, so 8 10 is light for me.
Started dukan mid Feb at 9 12. Got to 9 0 by mid April and 2 weeks off diet in April as was on holiday. Got to 8 10 by beginning of June and have maintained since then. Currently 8 9 but not trying to loose (ie have been doing consolidation diet since beginning of June - although usually have 2 pieces of fruit a day not one, and don't do protein only Thursday unless above 8 10 on Thursday morning!)
I am now a size 8, with around 20% body fat (very toned), I don't think it would be a good idea to loose more.
heinz don't do WW with a protein thursday, wouldn't work, would be fine for maintenance but I don't think it would get you over a plateau.
However no need to follow dukan strictly either, its about totally cutting out: a) the refined carbs - sugar (including honey etc), white flour, pasta, fruit juice, white rice, and all processed foods
That might be enough to get you over the plateau - but if it isn't then try cutting:
b) anything else that will spike your insulin levels - fruit, wholegrains, starchy veggies (carrots, parnsip, peas, corn), pulses, even dairy
Clearly you wouldn't want to cut out b) type foods for that long, and they'd be the first to reintroduce when you reached your target.
re: costs I don't think its that expensive, I eat a lot of: - tesco's own brand cottage cheese - tesco's own brand fat free yoghurt & fromage frais - tesco value eggs - tesco frozen white fish (coley, haddock) - chicken and turkey breasts - tins of tuna - buy on offer - tins of sardines, mackeral etc
I don't eat much meat - probably only a couple of times a week max. And even then usually mince.
I don't do low carb pasta or anything similar. I prefer to avoid processed foods, I think eating "clean" is the best way to loose and maintain weight loss and most low carb foods come up this category.