Careful on that one. As I understand it it's not an offence to remove an obstruction if you come across one but it is illegal to head out with the intent to do so. An anomaly perhaps and I may be mistaken but I think that's the way it is. I suppose it makes sense from one perspective - if you come across it you can remove it, if you know it's there in advance you should report it and let the authorities deal. Whether or not they will could be another matter altogether.