More and more police forces and government agencies are exploring the potential of unmanned drones for covert aerial surveillance, security, or emergency operations across the UK, the Guardian has learned.

The Serious Organised Crime Agency (Soca), which works closely with police forces and MI5, published an unusually detailed public tender notice in the summer requesting submissions from suppliers of airborne observation "platforms" that can be adapted for "target acquisition" and intelligence-gathering.

The proposal comes as the use of helicopter microdrones for law enforcement spreads. At least four forces – Merseyside, Essex, Staffordshire and British Transport police – have bought or used them.

Several government bodies, including the Environment Agency, have examined similar systems, while the fire services in the West Midlands and South Wales launch them as miniature spotter planes above major blazes. Some are operated commercially for aerial photography.

Microdrones can be fitted with video cameras, thermal imaging devices, radiation detectors, mobile-phone jammers and air sampling devices. Hovering at heights of around 60 metres, they are said by manufacturers to be virtually invisible from the ground.

This week the Civil Aviation Authority issued fresh advice about unmanned aerial vehicles (UAVs) for surveillance, warning that they must be licensed when flown within 50 metres of a person, property or structure.

"In the past we have seen people seriously injured or even killed by model aircraft," the authority said, "and, now that small, unmanned aircraft are becoming more readily available and simpler to fly, we need to avoid any similar incidents."

The CAA has contacted distributors to explain the rules for using "small, unmanned surveillance aircraft" in the UK. One senior police source said there was a serious risk that criminals might shoot remote-controlled drones out of the sky.

Soca's efforts are focused on tackling organised gangs involved in drug smuggling, human trafficking, gun crime, money laundering and identity theft. Often described as Britain's FBI, the organisation is led by Sir Ian Andrews, a former senior Ministry of Defence official.

The agency's request for bids is entitled "UK-London: intelligence, surveillance, target acquisition and reconnaissance". It proposes the use of both conventional planes and UAVs for a national air patrol service. The document suggests the surveillance contract could be put out to a private company.

The tender seeks information on "a fully serviced, airborne, surveillance-ready platform for covert observation". Drones, or planes, should be available for deployment within two hours of orders for "urgent taskings". Missions lasting up to five hours and night-flying are anticipated. "Low noise signature and unobtrusive profile" as well as a "discreet while accessible operating base" are said to be desirable features of any future aerial security system.

Pictures from onboard cameras and thermal-imaging equipment should be capable of being beamed down to "command and control rooms" as live, Soca's tender specifies. The agency adds that it "welcomes information from potential suppliers with regard to any UAV technology options".

Earlier this year the Guardian revealed that Kent police had expressed an interest in using drones for border and maritime security and other surveillance purposes.

Speaking on behalf of the Association of Chief Police Officers, ACC Allyn Thomas of Kent police confirmed that Staffordshire, Merseyide and Essex were using drones. "It is a cheaper option [than helicopters]," he said, "along with the opportunity to use the drones when cloud base cover makes it impossible for the conventional air support to fly."

Merseyside police had to suspend flights of a miniature helicopter drone it used in a successful manhunt earlier this year after the CAA announced that the force had not sought a licence to operate the system. It has since been given formal permission to resume flights.

The Soca tender, however, is the first formal confirmation of official interest in using the technology for police surveillance nationwide.

An agency spokesman said: "Soca's targets include the most determined criminals attacking the UK. It's unsurprising that in tackling drug trafficking, people trafficking and kidnap we look at the very latest technology. A purchase is not an automatic outcome of a procurement exercise."

Mark Lawrence, director of Air Robot UK, said: "UAVs will, to an extent, replace helicopters. Our air robots cost £30,000 compared with £10m for a fully equipped modern helicopter. We have even been asked to put weapons on them but I'm not interested in getting involved in that."

The UKBA has told the Guardian that it has "followed the development of unmanned aerial vehicles (drones) for the purpose of border surveillance and co-operated with other UK law enforcement agencies to examine their potential.

"[We] do not rule out the use of drones at some time in the future if they can be shown to provide a value for money increase in our border security."