Does an increasing migrant presence contribute to political radicalization of societies?

It depends on the degree of assimilation. The problem is the clash of cultures. The liberal view is that the hosting society has to make concessions. But it is equally true for the migrant society.

When a woman in London is hounded out of where she has lived for years because she is verbally abused for buying alcohol; or a native British boy is told by his Asian girlfriend not to walk her any further towards home because someone might see --- then resentment is fostered. Of course there's abuse the other way too, but the point is that assimilation is a 2-way thing.

And when well-meaning indigenous people get snubbed it is natural for resentment to occur.

And if mainstream political parties don't address these problems and instead talk in generalised platitudes then the door is wide open for more radical, single-issue politics to rise.