Well after getting some advice from a professional photographer I have took the plunge and ordered a Canon 17-40mm L series lens. I have always wanted a wide angel lens and after a bit of reading and seeing this seems to get good reviews for the price. I like the fact the lens takes the same diameter filters as my Canon 100-400mm lens that I have, so can swap polariser filters without spending more money.
Will let you's know how i get on, my first task once it arrives is to go out and take the same photo i took with my sigma 24-70 lens in the woods.
Sigma 24-70
Canon 14-70mm due soon