From your narrative you can argue that the location of the shed is a legal nuisance. It blocks your light and your enjoyment of your own garden. Have your lawyer issue a letter insisting that the shed is removed from that location. If they refuse or ignore the letter you can go to court, I think you will will and you could therefore claim most of your legal costs again. Happy to discuss. I hope that helps. Please leave a positive rating so that I am credited for my time.