Several years ago in a magazine/newspaper in the U.S., FarmShow, they had an article on a gentleman Bill Kreitzer who came up with a method of planting earthworms. Yes..planting earthworms. He developed a way to encapsulate the cocoons and allow them to be planted by hand and with machinery. He calls them vermipods. I ordered some for my garden (about 400 of them for a $100 US). They really do work as advertised. I just kept them in the refrigerator after I received them and planted them as I planted my seeds. I figure I get a little extra yield short- and long-term each time I planted one from not only the castings in the soil but from the extra aeration. Not sure if you can get them in the UK due to agricultural restrictions, but thought you might want to read about it. I think it is quite interesting. His websites are http://www.vermipod.com/ and http://www.billkreitzer.com/.
Steve