A young couple painted as EU flags protest on outside Downing Street against the United Kingdom's decision to leave the EU following the referendum on June 24, 2016 in London, United Kingdom.
A young couple painted as EU flags protest on outside Downing Street against the United Kingdom's decision to leave the EU following the referendum on June 24, 2016 in London, United Kingdom. - 

Brexit was in large part driven by an anti-immigration backlash, but exactly what kind of immigration was in the firing line?

Not just the migrants who have been in our headlines for the last year, the flow of refugees moving out of Syria and the Middle East and crossing in boats and trucks to Europe.

The target for this hardened stance on immigration was Europe itself: in particular, Eastern Europeans from countries like Poland, who have been moving to Britain in large numbers over the past decade or so.

In 2004, 10 new countries joined an expanded European Union, including Hungary, Poland and the Czech Republic. Migration Watch UK calls this a "watershed moment" for European migration because it opened up the U.K. — and its labor market — to the citizens of these countries.

Then in 2007, Romania and Bulgaria joined the EU as expansion continued, and people from these countries made their way to the U.K. as well.

Using their right to freedom of movement within the EU, many from Eastern Europe came to Britain in search of better jobs and wages. During these years, the phenomenon of the "Polish plumber" came about, as many hired Polish tradesmen to fix up houses and paint apartments — keeping wages low, some argued, for other workers.

In recent years, Britain has also seen the arrival of many from Southern Europe. As countries like Spain and Portugal were hard hit by recession in 2008, more people, and especially young people from these countries, moved to the U.K. to look for work.

But immigration also became fodder for right-of-center tabloid newspapers to attack what they say is mass immigration from the EU. It became an increasingly polarizing debate as many Brits wanted the government to put stronger curbs or limits on immigration to keep control of the numbers allowed into the country.

Between 2003 and 2015, there was an increase of almost 2 million people living in the U.K. who were born in other EU countries.

It would seem that simmering resentment against mass immigration from Europe has now expressed itself vociferously at the ballot box.