I'm thinking of doing the Exante 1200 cal diet during the week, having one or 2 600 days and then one or two slightly higher days at the weekend.   
The reason for this is I have a lot of packs to use up, the convenience during the working day of packs is great and it still allows me enough cals to exercise.   
I'm thinking something like  
Mon - 1200 (3 packs & 400-600 cal meal) 
Tues - 600 (3 packs), weigh in 
Wed - 1200 
 Thurs - 1200 
Fri - 1800 
Sat - 1800 
Sun - 600  
That averages out to 1200 a day, uses up my packs, allows exercise and gets me in the habit of 5:2.  I'm going to try it for 2 weeks and see. Fingers crossed!
Right, no more messing. I'll do a weigh in on Tues, then this for 2 weeks with daily exercise, then record my results at the end. I do like a nice clear short term goal.
I'd like to move to a clean, sugar free diet without counting on non fast days eventually but I need to get rid of some of these packs first! Plus this will get me into some good habits re weekends & evening meals, and then my next goal can be sorting breakfasts & lunches!