How did they cross the English channel? Did they have boats? Wouldn’t there be evidence of boats?
Leather hulled wood boats after 4,500 years? If one got buried in a peat bog it might be found intact, but otherwise little or no chance. There’s ample evidence of migration and trade from Europe into Ireland and Britain even earlier than this, but it consists of the usual kinds of durable artifacts like pottery archaeologists customarily deal in.
There may have been so much Polar ice that there was a land bridge between the two countries. No boats would have been needed.
I’d think boats would be an excellent suspicion. Any remains would likely be offshore, underwater due to sea level rise after the end of the ice age, provided they’re in an environment conducive to the survival of such artifacts. Some areas have very few artifacts beyond those made of stone or noncorrosive metal, for instance here the red clay soil is very acidic. Even known graves from 400 years ago contain little other than bones. Wood would be long gone.