A futuristic pilotless stealth fighter – the most technologically advanced combat aircraft ever produced in Britain – has passed its first ever test flights in a major milestone towards taking to the skies in combat, defence chiefs have announced.

The giant-sized drone, approximately 12 metres long with a 10-metre wingspan, has been codenamed Taranis – and is so secret that few details have emerged until now.

Footage of the unmanned aircraft in flight was shown for the first time in public at a briefing by the Ministry of Defence and BAE Systems at the Royal Academy of Engineering in London.

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The first ever test flights of the aircraft, dubbed an “unmanned combat vehicle demonstrator”, took place in August at a secret location, understood to be Australia.

Nigel Whitehead, group managing director of BAE Systems, refused to disclose the actual number of flights made but confirmed they had been at different altitudes and speeds, lasting up to an hour at a time.

“The aircraft has been designed to demonstrate the UK’s ability to create an unmanned air system which, under the control of a human operator, is capable of undertaking sustained surveillance, marking targets, gathering intelligence, deterring adversaries and carrying out strikes,” he said.

The development and deployment of a new generation of drones “is a dangerous expansion similar to the development of ‘First Strike’ nuclear weapons that brought the world to the brink of disaster during the Cold War,” warned Chris Cole, who runs the website Drone Wars UK. Drones such as Taranis “make the world a more dangerous place,” he added.

The use of US drones has become increasingly controversial. Last October United Nations human rights experts warned that a world where “multiple states use such weapons in secrecy” was a “less secure world”.

Reports have suggested that more than 2,371 people have died from drone strikes in Pakistan since 2006.

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But Mr Whitehead, who hailed the Taranis test flights as “a major landmark” for British aviation and an “extraordinary achievement in British engineering”, said the project is “vitally important” for the future of Britain’s defence sector. The flights “ surpassed our expectations in every way” and “prove industry has the ability to design and build an unmanned stealth combat aircraft,” he added.

Ground testing of the Taranis aircraft began in 2010, and runway trials were carried out last April. It was then shipped to an overseas test range, where the first flight took place in August.

There have been “significant challenges” in getting to this point, he admitted. The budget has soared by 50 per cent in the past eight years. A cost of £124.5m was cited when the Taranis project began in 2006, but it now stands at £185m.

The defence contractors QinetiQ, Rolls-Royce and GE Aviation are involved in the BAE-led consortium for the MoD, which draws on the expertise of scientists, aerodynamicists and systems engineers from 250 UK companies. Taranis was formally unveiled in July 2010 but only a small number of scientists and engineers have been given full access, on a need-to-know basis, to the top secret aircraft.

The stealth jet does not have a tail and looks more like a UFO than a potential addition to the RAF fleet.

It has been built to enter hostile airspace undetected and unleash missiles against enemy targets. Its designers boast that it can search for and destroy enemy targets, dodge incoming missiles and defend itself against enemy aircraft without the need of human intervention.

Although it does not yet have a functioning weapons bay, it will be able to carry a series of armaments on board including missiles and laser-guided bombs.

A BAE spokesperson told The Independent “humans would be able to programme these aircraft however they wanted”, but stressed that a controller will monitor the aircraft “at all times” and “can force a landing in case of an issue”.

Most details of the technology remain classified. The briefing was the first in four years, and workers at the BAE Systems’ military aircraft factory in Warton, Lancashire, are subject to extensive security checks and have to sign the official secrets act.

Taranis is the “most advanced air system yet conceived, designed, and built in the UK”, according to Philip Dunne, minister for defence equipment, support and technology.

Mr Dunne cited “military reasons” for the secrecy behind the project. “Taranis includes some technological advantages that this country wants to keep control of,” he added.

Air Vice-Marshal Sue Gray, the director of combat air at defence equipment and support, told The Independent: “although the combat aircraft can ‘fly itself’, it will not be used in that way, and cannot make up its own missions”.

Why the code name? Thunder God

Taranis was the Celtic god of the heavens, more commonly known as the thunder god.

The word, an appropriate name for such an aircraft, has its origins in the Breton language, derived from the words “taraniñ” and “taran”, meaning “to thunder” and “thunder”.

When provoked, Taranis could bring the fury of the skies down against those whom had angered him.

The Roman emperor Julius Ceasar compared Taranis, who was the thunder and storm god of the Celts of Gaul, to the Roman god Jupiter.

Jonathan Owen