The two huge Russian Tu-95 bombers, known by fighter pilots as bears, flew across one of the busiest civilian flightpaths in Europe and had their transponders turned off, meaning that they could only be detected by radar and would have been invisible on regular air traffic control systems.
The UK's air traffic controller, Nats, was forced to re-route commercial flights as a result. The decision was a "precautionary measure," a government official said.
The bombers — whose distinctive outline once made them one of the most recognisable symbols of the cold war — were initially intercepted by Norwegian fighters after taking off from Russia. They flew south from Norway over the North Sea towards UK airspace, continuing down the Channel and then along France's Atlantic coast.
Military officials and politicians across Nato have become increasingly concerned about Russia's provocative aerial sorties.
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An SAS civilian airliner taking off from Copenhagen in March narrowly avoided collision with a Russian spyplane south of Stockholm.
Nato countries saw a threefold increase in provocative Russian activity in the skies last year. In Britain, RAF fighters have had to be scrambled once a month on average since tensions with Moscow began to rise.
"Russian aircraft manoeuvres are part of an increasing pattern of out of area operations by Russian aircraft," the Foreign Office said.
Jock Lowe, a former head of flight operations at British Airways, said the incident over the Channel this week was a marked departure from the tactics of the Soviet air force at the height of the cold war.
In the 1970s and 1980s, Tu-95 long-range bombers would test UK air defence over the North Sea, often performing dummy bombing runs but they did not come as far south as the Channel.
"During the cold war the Russian bombers never came near the airways this far south," Mr Lowe said.