Former military leaders have expressed their concern over the UK's ability to defend itself against a Russian attack, as the Government was accused by a parliamentary inquiry of "sleep-walking" into the crisis over Ukraine.
Earlier this week RAF fighters were scrambled after two Russian bear bombers were spotted off the coast of Cornwall.
The Typhoon jets, from RAF Coningsby in Lincolnshire, escorted the Russian aircraft which were flying in international airspace close to the UK on Wednesday afternoon.
In light of the incident former head of the RAF Sir Michael Graydon told the Daily Mail he doubts whether Britain could cope with a shooting war against Russia and claimed their actions were "provocative".
He told the paper: "We are at half the capabilities we had previously. They fly in these regions to check our air defences and have probably worked out we are not as sharp as we were. They know it is provocative and they are doing it at a time when defence in the west is pretty wet compared to where they are."
Air Commodore Andrew Lambert, former director of defence studies for the RAF, said the UK's Typhoon jets, while a good aircraft, would be "overwhelmed" by an attack from Russia because they are small in numbers.
Yesterday David Cameron said Moscow appeared to be trying to make "some sort of a point" with the latest incursion by Russian warplanes. "I think what this episode demonstrates is that we do have the fast jets, the pilots, the systems in place to protect the United Kingdom," he said during an event at Felixstowe in Suffolk. "I suspect what's happening here is that the Russians are trying to make some sort of a point and I don't think we should dignify it with too much of a response."
Sir Michael told BBC Radio 4's Today programme: "There's absolutely no reason why the Russians shouldn't fly their aircraft around the United Kingdom, but the fact that they've chosen to do it at this time - when Ukraine is in the news - is making a point. The Prime Minister is quite right. They are making a point. It is provocative. I would have thought in a world in which we looked stronger, appeared more resolute, they would be more reluctant to do that."
Former UK ambassador to Moscow Sir Andrew Wood told Today: "It's a dangerous moment because Russia is a state of, in a sense, frozen anarchy. It's not a proper state. What they've done in Ukraine is to begin an adventure. They don't know how to end it, so there is some danger that their frustrations there will overspill into other areas.
"The Baltic states have been under pressure from Russia. But the majority of Russian-speaking citizens of those Baltic states actually do not want change. They are not emigrating to Russia. They would rather be in the EU and they would rather come to the West freely, which they do."
Cameron and the government have been criticised for a "catastrophic misreading" of mood by European diplomats in the run-up to the stand-off between Russia and the West by the EU Committee of the House of Lords on Friday morning.
Despite Britain's role as one of the signatories to an international agreement assuring the territorial integrity of Ukraine, it said the Government "has not been as active or as visible as it could have been" in seeking to resolve the crisis.
In a damning indictment of EU diplomacy, the committee said a decline in expertise on Russia in the Foreign and Commonwealth Office (FCO) and other EU foreign ministries had left them ill-equipped to formulate an "authoritative response".
It said for too long the EU's relationship with Moscow had been based on the "optimistic premise" that Russia was on a trajectory to becoming a democratic country.
The result was a failure to appreciate the depth of Russian hostility when the EU opened talks which aimed at establishing an "association agreement" with Ukraine in 2013.
"It (the committee) believes that the EU, and by implication the UK, was guilty of sleep-walking into this crisis," said the committee chairman, Lord Tugendhat.
"The lack of robust analytical capacity, in both the UK and the EU, effectively led to a catastrophic misreading of the mood in the run-up to the crisis."
The committee said that as one of four signatories to the 1994 Budapest Memorandum which pledged to respect Ukraine's territorial integrity, there had been a particular responsibility on the UK. "The Government has not been as active or as visible on this issue as it could have been," it said.
It said the FCO now needed to look at how it could rebuild its lost analytical capability on Russia. "While there has been an increase in staff at the FCO to deal with Ukraine and Russia, we have not seen evidence that this uplift is part of a long-term rebuilding of deep knowledge of the political and local context in Russia and the region," it said. "We recommend that the FCO should review how its diplomats and other officials can regain this expertise."
An FCO spokeswoman said no one could have predicted the scale of the "unjustifiable and illegal" Russian intervention in eastern Ukraine. She added: "The blame lies squarely with the pro-Russian separatists, backed by the Russian authorities, not with an association agreement between the EU and Ukraine which had been under negotiation for more than seven years before Russia decided to illegally invade and then annex part of its neighbour. If the Ukrainian people want a closer social, economic and political relationship with the EU, that is for the people of Ukraine to decide, not Russia.
"The UK has played a leading role in supporting Ukraine's right to chart its own future by ensuring that the EU imposed tough sanctions on Russia for seeking to dictate these choices. Ultimately the reforms to which Ukraine has committed itself as part of the Association Agreement process will help to build a stronger Ukraine that is better able to withstand external pressure."
She also said the FCO agreed with the committee that the EU must ratchet up sanctions if the situation in Ukraine worsens. She went on: "The Prime Minister made that position very clear at last week's EU summit, ensuring as a first step that additional sanctions on individuals involved in the destabilisation of eastern Ukraine came into force as planned on Monday.
"That is in keeping with the firm approach we have taken in response to Russia's intervention in Ukraine from the outset, and which it is now essential be maintained. The FCO has strengthened its expertise on Russia and the region and will continue working to ensure a strong and united response to Russian aggression."
The findings come as a further blow to David Cameron after Britain's former senior Nato commander, General Sir Richard Shirreff, said the Prime Minister had become a diplomatic "irrelevance" in the crisis.