Russia has dismissed claims its planes caused "disruption to civil aviation" in the UK this week, saying its actions were not "threatening" or "disruptive".
The UK Foreign Office said the Russian planes, which came near UK airspace on Wednesday before being "escorted" by RAF jets, were "part of an increasing pattern of out-of-area operations".
Russia's ambassador to the UK said the concerns were "not understandable".
He insisted the patrols were "routine" and met "international legal norms".
Typhoon fighters were scrambled from RAF Lossiemouth and RAF Coningsby to escort the Russian aircraft, and the RAF said the mission lasted 12 hours.
The Foreign Office refused to give details of the disruption to civil aviation.
BBC defence correspondent Jonathan Beale said the Russian planes - two Tu-95 Bear H bombers - came within 25 miles of the UK.
They travelled from the north, past the west coast of Ireland and to the English Channel before turning and going back the way they had come, he said.
He said the bombers did not file a flight plan, did not have their transponders switched on and "weren't talking to air traffic control".
In a statement, the Russian embassy in the UK said ambassador Alexander Yakovenko had met with British officials to discuss the issue.
The statement said: "This flight (as all other routine flights of the Russian military aircraft) was carried out in strict compliance with the international legal norms including international flight rules and regulations, without violation of other countries' airspace, therefore it cannot be regarded as threatening, destabilising or disruptive."
In response to a recent parliamentary question, the Ministry of Defence disclosed the number of days when Quick Reaction Alert flights were launched against Russian military aircraft
This is the latest in a series of similar incidents involving Russian aircraft. Last month Foreign Secretary Philip Hammond said the UK was concerned about the "extremely aggressive probing" of its airspace by Russia.
In a statement on the RAF website, one of the controllers involved in the mission said: "Thanks to our integration with air defence systems across Nato, we were able to begin mission planning early and therefore were ready to act in good time."
'Strutting their stuff'
The controller added: "The operations room was both calm and focused.
"We constantly train for these scenarios so that we are well rehearsed and ready to maintain the integrity of our airspace."
Former RAF pilot Andrew Brookes, who is a fellow at defence think tank The Royal United Services Institute, told BBC Radio 4's Today programme similar incidents had happened in other parts of the world.
He added: "The Russians are coming back on to the world stage, they've cranked up an air force that they have neglected for many years, and they are basically strutting their stuff around the globe."
Nato Secretary General Jens Stoltenberg said there had been a sharp increase in the number of times Russian planes were intercepted by members.
He said: "Last year, allied aircraft intercepted Russian planes over 400 times. Over 150 of these intercepts were conducted by Nato's Baltic air policing mission. That's about four times as many as in 2013. So we are staying vigilant."