It has been posted before, but the thread title is very misleading, it has "NOT" been decriminilised in the UK. The sentencing guidelines are set to change at the end of feb, what it does mean is that someone growing less than 9 plants with an average of 40g per plant, is now much more likely to get a fine and community service orders rather than jail time if it is a hobby grow. If its connected with dealing in any way at all you will still go to prison.
The hope is that due to the new guidelines Judges will no longer be able to hand down Draconian sentences for minor offences as they will now be open to immediate appeal if they do. If this is seen by the CPS (Crown Prosecution Service) to be a waste of money the hope is that the police will no longer waste their time on pursuing minor cases, as without interest from the CPS they will not go to court in the first place.
Note
It is still very much Illegal to grow in the UK and as stated above the Police are still fully intitled to kick in your door and haul you away and add a criminal conviction to your record!.