What are they???
 

I have searched the internet far and wide but cannot find out what the pest that is in my soil can be, please help!!!
In isolated pockets of ground in my allotment there is a very small pest, it so far has appeared in Potatoes, tomatoes, Chinese cabbage roots and leeks. They look like a centipede with out legs, are about 5mm long, 1mm thick. They have a sort of clear whitish front end with small antenna then almost stripped dark and light the rest of the body.
They appear in the part of the plant touching or in the soil and in great numbers but only in isolated patches.
I have had the allotment 3 years, it was not badly over grown and the patches where the “mini beast” appears are seemingly random i.e. not related to grass or specific vegetation.
Does anyone know what they are and what I can do about them?