The Criminal Justice Act 2003 says that if you plead guilty to an offence then you are entitled to credit in the form of a reduced sentence as compared to the sentence you would have received had you been found guilty after a trial. The amount of credit you are entitled to depends on at what stage of the proceedings you plead guilty. In general, you will receive a reduction of 1/3rd if you plead guilty at the very first oppotunity. The later in the proceedings that you plead guilty, the less credit you are entitled to. The credit reduces to just 10% if you plead guilty at the last minute.