THE Government has insisted that the location of dozens of Hampshire fields used to grow the raw materials for heroin must stay secret - to stop people stealing the controversial crop.

The Home Office rejected a Freedom of Information request lodged by the Daily Echo to find out the precise locations of 26 sites in the county used to cultivate opium poppies for medicinal use last year.

The poppies, from which the illegal Class A drug heroin is derived, are usedto produce legal morphine, which is used by the NHS to relieve pain.

In February, the Daily Echo revealed that Hampshire was the UK's capital for opium production, with the county's 2007 crop, taking up 1,238 hectares, almost as large as the rest of the UK's put together.

By comparison, the second biggest crop, in Lincolnshire, was just 445 hectares in size.

After reporting the existence of the 26 secret sites for the first time, following a Parliamentary written answer by Home Office Minister Vernon Coaker, the Daily Echo asked for a detailed list of their locations, but the Home Office has revealed it is "not obliged" to reveal the information.

A response to the FOI request, written by a Home Office official, said the department had decided it was in the public interest to keep the information under wraps because disclosure "would be likely to prejudice the prevention of crime".

He explained: "In view of the nature of the crop being cultivated, disclosing precise details of the growing sites could encourage the commission of crime through trespass and pilferage of the crop."

Anyone can grow opium poppies because the process is not controlled by the Misuse of Drugs legislation, but any processing of the plant to extract narcotic material is controlled and can only be carried out under licence.

The farmers involved are not obliged to inform local authorities of the nature of their crop but are advised to present a letter sent to them by the Home Office to local police.