@Menopausalsourpuss
"I am 56 and don't remember there ever being an issue with young male illegal migrants until the last 20 or so years (and none of these sort of attacks either - the world was much safer). "
It's simply due to numbers of immigrants.
From 1980 to 2000 average annual net immigration was around 50k people per year coming into the UK which is easy to absorb and provides a net benefit to the economy by quickly providing hard to fill roles etc.
However over the last decade it has been over 300k per year and in the last three years over 800k per year. That roughly the population of Newcastle or Liverpool every year.
With more people means statistically that there will be more crime involving immigrants. As well of course adding pressure on infrastructure, housing, healthcare, education etc.