There was an extensive discussion on earthworms last year and it was mentioned that earthworms originally did not exist where the last glacier extended over approximately 1/2 of North America, and that imported/invasive/escaped earthworms are displacing native fauna and destroying native flora. In some northern states, conservation-minded folks are intentionally eradicating earthworms from their gardens.
Can't remember if you mentioned where you're from elsewhere, but if "new forest" is in the northern half of the Northern Hemisphere, you may live where earthworms are naturally scarce.... In other words, it may be a good idea to do some research before INTRODUCING earthworms to your area.
That said, earthworms dig deeper when soil surfaces are dry, and rise to the surface to escape drowning when the soil is saturated. People say they LOVE used coffee grounds. They love organic material and I can tell you that all my sheet mulched areas are teeming with earthworms. I was relieved to verify that I live south of the "glacier zone".