I have an investment property which has a single story flat roofed extension to the rear. The property immediatly behind has built on an extension and has placed windows (not on their planning permission) in their 2nd floor level. If they ever get the right to keep them then we will never be able to go up another floor. I do not want to ask them to remove the windows while they are not bothering us, but we do not want to be stiffled in the future. Can anyone tell me at what stage (if ever) they would be entitled to retain the windows. They have offered to give us a written undertaking that they will remove them if we ever need them to.