Hi Helen
I have exactly the same mole/freckle on my foot. I freaked out ! I was told that it is a parallel furrow mole (which are found on the hands and soles of feet typically and are harmless pigmentation) the pigment distributes itself in the furrows of the skin, as the surface of the skin on the hands and feet are different. Obviously nobody can take diagnose over a forum but I used to get so obsessed with the one on my foot and watched it grow and settle before breaking down in the doctors office. Look at my other posts on moles if that helps :-)
All the best
Stu