Home Minister Rajnath Singh has said that the Centre has issued an advisory to release undertrial prisoners who have served half of their maximum punishment provided under the law. <br />''<br />''<br />''He said, some state governments have started with the compliance on the advisory. There are about four lakh prisoners in jails and out of them about half are undertrials. <br />''<br />''He was speaking at a function at the district court in Lucknow yesterday to administer oath to newly elected office bearers of the Central Bar Association. <br />''<br />''<br />''The minister said, centre has abolished nearly 1,500 obsolete laws which have lost their efficacy.<br />''<br />