Presumably we are talking UK here? Any habitable dwelling must have the approval of the local planning dept and carried out under the inspection by building control officers.
From what you have described, I am surprised that they have granted permission for a building that overlooks your property but the only way to tell is to visit the planning dept and ask to see the file.
This may or may not be of use to you ...
RIGHT OF LIGHT
A Right of Light is protected in England and Wales under common law, adverse possession or by the Prescription Act 1832. Unlike right to freedom from smell and noise, a Right of Light has to be acquired before it can be enforced.
Natural light is a commodity that can be bought, sold or even transferred between parties. Rights can be registered, granted by deed or simply acquired by having a minimum of 20 years enjoyment of light through a window or opening. Once a window has received over 20 years of unobstructed daylight, it automatically earns itself a Right of Light. Such rights are, for Land Registration purposes, overriding interests. They are valid whether or not they are registered on the title deeds to the property which claims the right.
A development may be prevented due to a Right of Light, even if Planning Permission has been granted by the Local Authority.
If a new building limits the amount of light coming in through a window and the level of light inside falls below the accepted level, then this constitutes an obstruction. Unless the owner of the affected window waives his rights he would be entitled to take legal action against the landowner if he considered that his light is being blocked.
To complicate matters further, the law recognises that some loss of light is acceptable and the fact that there is less light does not necessarily give a land owner a right to complain.
The general rules are:
1) The reduction in light must make the property less fit than it was for its purpose.
2) The amount of "appropriate" light may vary depending upon building, use and even region.
3) The amount of light considered to be sufficient will tend to increase as standards of living and expectations increase.
Any kind of 'development' can potentially block light. For instance:
A new shed
Part of a new housing or commercial development.
This may prevent a proposal from the erection