Do prosecutors go easier on you if pleading guilt right away?

The Prosecution don't have any interest in getting you a heavy sentence. Their main concern is to gain a conviction and to be able to file the case away. They are called upon to give the brief facts of the case and obviously they are going to mention the fact that you admitted that you were in possession with intent to supply, but don't forget that your barrister has the last word and will fall over backwards to point out how cooperative you have been and all the positive things (s)he can think of in your favour. You will certainly be given credit in sentencing for your plea of guilty.