Cramp in toes - any tips?

Can anyone shed any light on a) why I get severe cramp in toes and b) how I can prevent it?

It wakes me up at night which is a pain but i can deal with that. However, it comes on when I'm at they gym and its excrutiating and it can remain for hours sometimes. I thought my trainers were slightly too big and it was making me "grip" the floor, alas, new trainers and it hung around for the whole training session! Coach is a brute so squats on tippy toes trying to shift it was an endurance test in itself.
Oh, and it was very cold last night - does that play a part?

Any tips/advice appreciated, thanks.