Hi JCJ!
The only difference with regard to the "routes" that you can take on LL is the amount of weight you have to lose.
I'm hoping the information that I give below is accurate, but I'm sure someone will correct me if it's not! ;-)
For example, if you have between 1st and 3st to lose (BMI between 25 and 29), you would be advised to go on LL Lite, which is three foodpacks and one meal from a carefully designed list of foods I think.
If you have over 3st to lose (BMI of 29 or over) you would go on the original LL programme for 14 weeks. I know you mentioned 12 weeks, but this is the recommendation from NICE that after 12 weeks you should be on a LCD for one week when you would increase your calories by having milk (although no one in my group were actually advised to do this be the LLC and I for one chose not to do it, but I only knew about it from here in all honesty!). You can then continue in this vein, having milk every 12 weeks.
LL say you will lose 3 stone in the 14 weeks (Foundation), and if this was all you had to lose you'd go on to RTM for the next 12 weeks, gradually introducing food and reducing packs. I actually lost around 5st in my Foundation, but still have approx 12lb to go, so I continue on in what the call Development - which is essentially the same as Foundation really!
Hope you decide to do LL - it's certainly life changing!