In a sense, he is kind of right to say Muslims did contribute to British society and culture.
They did.
However, while they still contribute the current shift has them doing it in a fairly negative way overall. Sure, gang fights are a thing around the world, and we can talk about societal disparities and such... but it seems England developed a sort of forced multiculturalism solidified with a hefty dose of gas-lighting.
Which is rather amusing when taking Merz recent comments on these issues in Germany: "a significant amount of illegal migrants bring antisemitism with them".
Now, in retrospect, will it be "explained" as "well in fact Merz was just saying there is more racism, because people in Germany are racist and they don't like foreigners, and therefore the influx of migrants makes them behaving in a more racist fashion"? Or that the antisemitism is brought by the migrants, who are antisemitic.
Anyway, that aside, and considering the post by the British Gov on "terrorist ideologies", the UK is not doing great.
But that's their problem. They keep on voting for it so... heh.