No, cannabis briefly became a Class C drug which did not make it legal, or even decriminalised. Class C drugs in the UK carry a theoretical penalty of 2 years in prison for possession and 14 for supply and production. Though the sentencing guidelines are nowhere close to that.
The police do have a system of "cannabis warnings" over here which treats being caught along the lines of an official "don't do this again" unless you're either a child, keep being caught, or the circumstances warrant a straight up arrest.
The police do have a system of "cannabis warnings" over here which treats being caught along the lines of an official "don't do this again" unless you're either a child, keep being caught, or the circumstances warrant a straight up arrest.