Around 3700 BCE,Ireland had a full fledged sedentary farming village society. In the three hundred years that followed, apparently due to a worsening climate, this society collapsed. The people of Ireland returned to a hunting and foraging method of food production where the island remained for about 1200 years. A return to sedentary farming didn't begin until around 2200 BCE. There may have been similar developments in Britain. Instances of a return to hunting and foraging after a brief period of farming, before an ultimate return to farming, driven by climate, are also known in Scandinavia thousands of years later.
Among other things this means that for much of Northern and Western Europe, an era of hunting and foraging was much more recent at the advent of the historical record than an estimate based upon the earliest Neolithic archaeological traces would suggest. It also suggests that the relationship between megalithic cultural remnants and food production method may be more nuanced than earlier analysis had suggested.