The two Russian Bear bombers were "escorted" by RAF jets, the MoD says (file photo)
RAF jets were scrambled on Wednesday after two Russian military aircraft were seen off the Cornwall coast, the Ministry of Defence has said.
The Russian Bear bombers did not enter sovereign airspace, it said.
On the same day, Defence Secretary Michael Fallon warned that Russia's President Putin posed a "real and present danger" to three Baltic states.
Prime Minister David Cameron said the Russian action should not be dignified with "too much of a response".
He added: "I think what this episode demonstrates is that we do have the fast jets, the pilots, the systems in place to protect the UK.
"I suspect the Russians were trying to make some sort of a point."
BBC political correspondent Ross Hawkins said the appearance of Russian aircraft near the UK coast was a show of strength from the Russians, and such incidents were carried out with political intent because they would be reported on.
Our correspondent said it was part of a trend which had seen Russian aircraft flying close to UK airspace and there had also been concern about similar incidents in Europe.
It comes amid increased concerns over Russian involvement in the conflict in Ukraine and suggestions of Russian President Vladimir Putin's potential future interference in Latvia, Lithuania and Estonia.
A ceasefire deal between government and pro-Russian rebel separatists in Ukraine was reached a week ago.
But battles around the strategic town of Debaltseve have seen the withdrawal of Ukrainian troops, while there was shelling in several places in eastern Ukraine, including the region's biggest city, Donetsk, on Thursday.
'New' Cold War
Russia has denied helping the separatists, but it has been accused repeatedly of sending weapons and troops and using propaganda to inflame tensions.
And Russia's UN ambassador Vitaly Churkin has labelled Ukraine's call for the deployment of UN peacekeepers in eastern Ukraine as a destructive move.
Mr Cameron has said rebels in eastern Ukraine are using Russian military hardware, and that Mr Putin must understand there would be "economic and financial consequences for many years to come" if he did not change his behaviour.
"They are modernising their conventional forces, they are modernising their nuclear forces and they are testing Nato, so we need to respond."
Mr Fallon also said the prospect of a new Cold War was "warming up".
"You have tanks and armour rolling across the Ukrainian border and you have an Estonian border guard who has been captured and not yet still returned."
He also said Russia was likely to use covert tactics such as those he said it had used to annex Crimea and during the current Ukraine conflict.
Mr Putin had also flown two other bombers "down the English Channel two weeks ago", Mr Fallon added.
"We had to scramble jets very quickly to see them off.
"It's the first time since the height of the Cold War, it's the first time that's happened."
Jonathan Marcus, BBC defence and diplomatic correspondent
The comments from Defence Secretary Michael Fallon are an indication of a fundamental shift in the Nato perception of the crisis in Ukraine.
Nato governments clearly believe that what began as a localised Ukraine problem that strained ties with Moscow has now become a Russia problem, and a Russia problem that is likely to persist for some time.
Ukraine is thus seen as a manifestation of a much broader policy shift on the part of the Russian President Vladimir Putin.
Mr Fallon's belief that there is indeed a potential threat to Nato territory - in particular the Baltic Republics - is widely shared; hence Nato's desire to underline in the most emphatic terms that its security guarantees to its members will be honoured in full.
Russian Foreign Ministry spokesman Alexander Lukashevich said Mr Fallon's comments went "beyond diplomatic ethics" and used "unacceptable terminology".
He also said Russia would "find a way to respond".
According to the Department for Transport, there was no record of disruption to civil aviation as a result of the bombers' presence on Wednesday.
The MoD said: "RAF Quick Reaction Alert Typhoon fighter aircraft were launched [on Wednesday] after Russian aircraft were identified flying close to UK airspace.
"The Russian planes were escorted by the RAF until they were out of the UK area of interest. At no time did the Russian military aircraft cross into UK sovereign airspace."
A similar incident occurred in January, when the UK Foreign Office said two Russian Tu-95 Bear H bombers flying near UK airspace had caused "disruption to civil aviation" and were also escorted by RAF jets while near UK airspace.
Deputy Prime Minister Nick Clegg said the latest incident "shows that we are of course living in a time of heightened tension with Russia... and we should remain vigilant at all times".