The first step, is really to amicably see if you can speak with your neighbour and perhaps ascertain why they have removed the fence. Potentially, they may be painting it or for preservation works, and it may be that it will be shortly installed later that day. If that doesn’t prove possible and perhaps your neighbours have removed it permanently, then what really needs to happen is that you need to ascertain who ultimately has ownership of that fence. If you do, then it may be the case that you write to your neighbour formally and ask that they place it back by a certain period of time. But if that doesn’t prove possible, then it maybe that you have to approach a solicitor and potentially ask that they write to them to reinstate the fence or otherwise, if that doesn’t prove possible and the fence is still out of place, then it may be that we apply to the court for an injunction for the fence to be put back in place.
