Thousands of staff at UK nuclear power stations have been told to spy on the private lives of workmates and inform on colleagues who might be “vulnerable” to blackmail or bribery by terrorists intent on getting access to Britain’s nuclear secrets and stocks of weapon-grade plutonium.

As part of the “security measures” nuclear power station staff are being asked to keep a watch on their colleagues’ love lives. They are also being told to keep tabs on colleagues they think may be using illegal drugs and even those travelling abroad.

The moves by the government’s nuclear security agency to step up the vetting of civilian nuclear workers have been condemned by trade unionists and critics as “Orwellian”. But the agency insists the measures are justified by the threat of terrorism.

The secretive Office for Civil Nuclear Security (OCNS) is charged with regulating security at 31 nuclear sites in the UK, including Dounreay in Caithness, Hunterston in North Ayrshire, Torness in East Lothian and Chapelcross in Dumfries and Galloway.

On Monday the government is due to give the green light to major new nuclear power stations in England and Wales. No plants are likely to be proposed in Scotland because of opposition from the Nationalist government in Holyrood.

In its latest annual report, the OCNS reveals that it provided security clearances for nearly 15,000 workers in 2008-09. Personal details of staff were vetted to try to ensure that they would not leak sensitive information which could render nuclear plants more vulnerable to attack.

But OCNS director, Roger Brunt, made it clear that he wanted to go further.

He says: “I would like to see all employees develop an awareness of how they can help identify and provide support for individuals holding a vetting clearance who may become vulnerable, for example, as a result of a change in personal circumstances.”

Mr Brunt pointed out that close colleagues were likely to be the first to notice any “unusual behaviour”. A system has been put in place requiring “the notification of relevant events such as a change of partner, new co-habitees, and travel overseas.”

Travelling abroad could make nuclear employees “the target of an attempt to gather intelligence”, Brunt cautioned. He has also introduced a “much stronger line” on the use of illegal

drugs because they “can make individuals subject to financial inducement or lead them to exercise misjudgement.”

But Dave Watson, Scottish organiser for the energy union Unison, warned that there were grave risks for human rights. “Workers take their privacy very seriously,” he told the Sunday Herald.

“Any suggestions that co-workers should become agents of surveillance are likely to be resisted strongly.”

Dr David Lowry, an independent consultant on nuclear security, pointed out that experts had long predicted that an increasing reliance on the nuclear industry would have dangerous implications for civil liberties due to the generation of electricity by power plants producing plutonium, which can be weaponised, as a by-product.

“As ministers in Westminster ramp up their plans for up to 11 new nuclear plants in England and Wales,” said Mr Lowry, “it seems that these predictions are now coming true. My concern is that in the rush to back new nuclear power stations, ministers are simply ignoring the unresolved difficulties with this unforgiving technology.”

Mr Brunt, however, denied that he was asking staff to “spy” on colleagues. “Noticing a shift in your employees’ or colleagues’ behaviour and taking the time to enquire after them is not spying but a natural caring response,” he said. “In the annual report, I was highlighting an important duty of care that line managers have towards their staff.”