Marijuana posession or Intent to supply?(U.K)

[Sky Walker]

I was just woundering if any of you guys know how, in the U.K, they decide weather of not it is simply posession or posession with intent to supply. I know that for posession you can get up to two years in prison but if charged with intent to supply the scentence goes up to 14 years! Madness I know but does anyone have any ideas how they prosecute growers or what they go by to determin weather it's for personal use or supply, e.g do they weigh the plants or just the bud from the plants or is it how many plants one might have or is it quite vauge and no one really knows?

Cheers in advance.