Thank you for your kind replies, I will use the links you have posted for me and see what happens next.....

Hi, newbie posting here, so I hope this is correct. My neighbour just blithely announced to me. "We're building a little house in the garden and we're going to live in it!". The location is right ( literally ) right beside my house on the boundary fence and underneath my bedroom windows. I suspect they are using their detached garage as the original location because otherwise previous developments to the main house take them over their permitted development allowance. I know garages can be used for other uses without planning permission, but surely I have some rights about this change of use when its so close to my house? The matter is not as simple as might appear, my two worst case scenarios are they turn the garage into a summerhouse and then encourage the teenagers of the household to hang out there... or they apply for planning permission to turn it into a development plot for an actual house and sell to developers. Have been worrying myself sick about it ever since they said it as we find neighbour noise really disturbing and the thought of them crashing about under my windows all the time is not a pleasant one. Also they are a bit nosy and like to eavesdrop if they can... Has anyone encountered cases like this before and can give advice? Many thanks , hope somebody can help me.......