OUR Finnish host—an MP guiding us around their glorious parliament—told us the Russian tsar liked his Finnish troops: "he said we were small and ugly, smelly and fierce."

The new tsar, Vladimir Putin, has discovered that today's Finns are taller, better nourished and infinitely more fragrant. But they're every bit as ferocious as their forebears.

I've spent the last week with cross-party Westminster colleagues finding out why Finland has decided to abandon neutrality and join NATO.

It's clear Ukraine has been the catalyst. The Finns have never trusted Russia, and with good reason.

They were part of the Russian Empire for a century, and Stalin, unreconciled to their 1917 independence, attacked his neighbour in 1938.

Incredibly, tiny Finland fought the Soviet Union to a standstill but had to cede huge amounts of territory and promise political neutrality to secure a tense peace.

Finland, a country with a population the size of Scotland, has spent the post-war years transforming itself into one of the most prosperous and best-educated countries in the world. It has a standard of living of which oil-rich Scotland has only ever dreamt.

And it's spent eye-watering amounts preparing for another Russian attack. Finnish males all do military service and few complain.

There are bunkers which can accommodate, feed, and give medical treatment to most of the population for weeks in the event of war.

And without nuclear weapons, the billions saved have gone into conventional forces to make Russia think twice about any future attack.

But why NATO? And why now? Across the political spectrum, there seems to be agreement that the security guarantee offered to all NATO states – attack one and you attack them all – is now needed to deter a rash and unpredictable Russian leader who, they think, would have no qualms about disregarding Finland's neutrality and whose intelligence briefings seem skewed to please rather than inform him, as his Ukraine adventure has shown.

Sweden, the Finns say, had to be pushed a little. Sweden doesn't have a border with Russia. But the Finns know their Western neighbour well. After all, they were part of the Swedish Empire too, and for centuries before they were ruled by Russia.

"But once we said we'd join, they decided to commit to NATO too," one MP told me. "Russian military jets already buzz Swedish airspace above Gotland in the Baltic. They decided they don't want to be isolated."

The Finns are used to a long waiting game. In their Helsinki parliament, five huge statues look down on parliamentarians. They are monumental in scale and glisten. But the gold, it turns out, is recent. Independent Finland couldn't afford gold statues and they were cast in plaster. The gold versions came later when Finland had the money to upgrade.

Was independence worth the wait, I asked? Any regrets that you're not still ruled from Stockholm? You cooperate so well. Our hosts laughed. "Ah, but these days we're independent and equal."