Garvan Walshe is a former National and International Security Policy Adviser to the Conservative Party. He now runs Brexit Analytics.

Just after the last Winter Olympics ended, armed men, carrying advanced equipment, lacking identifying patches on their crisp green uniforms, and boasting the impressive discipline appropriate to elite soldiery began to appear across the Crimean peninsula. They were, of course, Russians, but the deception caught the world off guard and allowed Moscow to present its take-over of Crimea (later approved in a rigged referendum) as a fait accompli.

A little later, similar armed men, albeit less disciplined, less crisply uniformed, and more diversely equipped began to appear in the Don valley, seized control of Luhansk and Donetsk, chased Ukrainian troops away from the border with Russia, and began to admit into the ominously named “Novorossiyya” supplies of war materiel and “volunteers”.

Ukraine had just had a revolution, the pro-Russian and obscenely corrupt Viktor Yanukovich having to flee rather than fight a civil war to stay on. Its army existed only on paper, capable only of protecting the presidential palace, and without much hope of even defending the capital. Eastern Ukraine is a large, flat and essentially indefensible plain. Russian armoured columns would face no natural obstacles until they reached the Dnipro river itself. Desperate plans were improvised for Polish forces at least to protect Lviv in the West (part of Poland between the wars, and the Austro-Hungarian empire before that, so not a course of action devoid of difficult historical echoes).

But the full-scale Russian invasion never came. With Western help and the money from Ukrainian oligarchs, a heroic defence was mounted. The shooting down of the MH17 airliner carrying medical researchers by a Russian-supplied anti-aircraft system solidified European opinion against Russia just as it appeared to be tiring of confronting Moscow. Two rounds of peace talks yielded agreements at Minsk that stabilised, but didn’t end, the fighting. The International Crisis Group now estimates that 10,000 have died on both sides.

This has led to the conclusion that Russia has been contained in Ukraine. Sure, Ukraine may have lost territory and people but Russia also lost a population sympathetic to their views that it could use to influence Kiev. Moscow, having had to contend with heavier resistance than it expected, has become content to treat Ukraine as another frozen conflict, and decided to flex its muscles in Syria instead.

But Glen Grant, a British military adviser to the Ukrainians for some years, thinks this is dangerously complacent. Writing in the Kyiv Post in January, he sounded an alarm. Putin’s military modernisation programme, he believes, is designed to reconquer Ukraine, and Ukraine has wasted the years and failed to reform its armed forces to successfully defend its territory.

His isn’t the universal view among Russia analysts, who often argue that the Russian military has not modernised as much as the Kremlin would have us believe. Thus, while Grant is right to point out that Ukraine has failed to adapt to the pressure of the war, they argue that Russia has not attained a state of Germanic efficiency (in this area even Germany isn’t Germanic: its new frigate has great difficulty staying afloat).

But the ‘Grant thesis’ is a risk to be taken seriously. When revisionist powers build up their militaries, they often find the temptation to use their shiny new equipment irresistible.

This presents an immediate practical mission for the UK, to intensify its efforts to reform and support the Ukrainian military. Rather than just assistance, this could be said to be an opportunity for knowledge exchange. Ukrainian forces have gained valuable experience of the kind of state-to-state conflict that the UK has not fought in years, and against Russian weaponry it has never faced before.

It is also, however, a wake-up call for UK strategic thinking. The UK no longer has the resources to act as a partner in the western Alliance with “global reach”. In dollar terms, the UK’s defence budget has fallen along with the pound. Unless radical increases in defence spending are planned, we need to concentrate our effort where it is most needed: in our immediate neighbourhood and on the two principal sources threats to our security, Russian revisionism and chronic instability in the Middle East.

Even within this more restricted mission, it may be necessary to concentrate more on the defence of Europe from Russia, and less on policing the mediterranean and the middle east: tasks in which other countries have a more immediate interest. In these straitened circumstances, it is worth asking whether a second aircraft carrier can be justified. In headier days the hope had been to build three Queen Elizabeth Class carriers, one of which would be operated jointly with France. This plan should be revived but for the second carrier, the Prince of Wales. (A name change might be in order, however: what better than calling it after of that successful Anglo-French warrior, William the Conqueror?)

The Russian state has returned as the most serious threat to British and European security. Even if Grant’s gloomy predictions do not come to pass, the possibility that they might should be used to give a renewed focus to British defence planning, particularly should Russia use the aftermath of this year’s World Cup to to spring a summer surprise.