John Reid, the home secretary, is planning a new official secrets law to punish intelligence officers who blow the whistle on government policy by leaking secret information. He wants longer jail sentences and the removal of a key legal defence of 'necessity' for whistleblowers. The crackdown is aimed at preventing cases such as that of Katharine Gun, a former translator at GCHQ, the government's eavesdropping centre, who leaked a memo showing that in the months before the Iraq war in 2003 the Americans wanted GCHQ's help in bugging the homes and offices of UN security council members. The government dropped its case against her after she threatened to use the necessity defence that she broke the law to prevent a greater 'crime' in the form of an invasion of Iraq. Ministers are also concerned at the growing number of leaks of sensitive documents by dissident officials, including those relating to the MI5 investigation into the July 7 bombings. It will be the first change to the official secrets legislation since 1989 when the government removed the right of whistleblowers to claim a defence of public interest.