A feather of disturbed water was all it took to reveal the presence of a Russian submarine off the west coast of Scotland.

Betrayed by its high-powered periscope, the vessel then disappeared, triggering a fruitless search that sent all manner of unwelcome messages to the Westminster Government.

Firstly, it is a reminder that the UK's armed forces lack a suitable maritime patrol aircraft after scrapping the Nimrod equivalent in 2011 and, secondly, the uncompromising message that Russia has the capacity to mount aggressive Cold War-style reconnaissance missions unhindered against Nato countries will have been noted in London.

The first issue was resolved by Nato allies sending their aircraft to Scotland to join the hunt. They included two US navy P-3 Orions, a Royal Canadian Air Force CP-140 Aurora and a Dassault Atlantique 2 of the French navy - but the problem of Russian aggression will be less easily resolved. Ever since Vladimir Putin returned to the presidency in 2012 he has made it his business to keep Nato on its toes by using his armed forces to further Russian interests across the world.

Last month, there was a similar Russian submarine scare in Swedish waters while at the same time Nato warplanes had to be scrambled to see off the incursion of more than 30 Russian aircraft over the Baltic. Further afield, four Russian warships were sighted off northern Australia's coast during the G20 summit in November. At the height of the Cold War such exercises and Nato's responses were commonplace as rival commanders tested the capabilities of their forces, frequently daring the other side to take greater risks.

But since the collapse of communism at the end of the 1990s, a "live and let live" atmosphere had prevailed. Russia even mothballed its powerful Typhoon class nuclear submarines and, under mutual defence agreements, both conventional and nuclear weapons have been destroyed. With the introduction of Nato's Partnership for Peace and the demilitarisation of central Europe, where the northern German plain would have become the main battleground if the Cold War had ever turned hot, confrontation between Russia and the West seemed to have become a thing of the past.

Russia's involvement in the affairs of Ukraine earlier this year and its support for the claims of the Crimean peninsula changed all that. When the West challenged Moscow's motives, especially after the shooting down of the Malaysian airliner during the summer, Putin made it clear that he would not allow his country to be pushed around. In the face of EU economic sanctions which have made an impact on the Russian economy, Moscow's expenditure on defence has increased substantially. This Friday sees the launch of a third Borei-class nuclear submarine, the K-551 Vladimir Monomakh, which carries 16 new-generation Bulava intercontinental ballistic missiles, each armed with 10 manoeuvrable warheads with sophisticated stealth capabilities, making it a formidable weapons system.

The slump in oil prices has slowed arms production in Russia but for the first time the country's defence expenditure has been higher than that of the US. According to the Stockholm International Peace Research Institute, it totalled $88 billion, an increase of 4.8% which will allow the Russian army to spend $705 million on replacing obsolete Soviet-era equipment. In the latest state-of-the-nation address, made on December 4 in St George's Hall in the Kremlin, Putin set out his stall by reminding delegates that Russian sovereignty was "a necessary condition for survival" and that he would not be moved by Western attempts to get involved in his country's dispute with Ukraine.

While claiming that Russia would not enter a new arms race, Putin went out of his way to remind the world that this did not make the country a soft touch. On the contrary, he boasted that "no-one will succeed in defeating Russia militarily", adding that "the more [Russians] retreat and justify ourselves, the more brazen our opponents become". The inference was clear: Putin does not want a new Iron Curtain, with Russia isolated as it was during the Cold War, but nor will he allow his country to be belittled. The unexpected and so far unexplained presence of the Russian submarine off the Scottish coast could be just one of many sallies against what Putin considers to be a hostile world.