Our neighbours a few years ago built an extension above their garage. The garage is directly on the border (not within their boundary). The extension has cut off natural light to the bathroom and kitchen. We naively did not object at the time as we simply did not consider the ramifications to us of the extension being built. For example, we now have to turn on lights during daytime hours when in the aforementioned rooms. This is both an inconvenience, an added cost and has a detrimental effect on the price of the property. Is there any way we can remedy this problem? Thank you.
Sadly I don't think there is. It is almost trying to shut the stable door after the horse has bolted. I feel sorry for you as it is difficult to see the impact of such extensions until they are erected, but even so, had you actually objected to the plans, it does not necessarily mean that they would have been turned down as you do not have rights to light/view automatically anymore.
By the 'garage is directly on the border' presumably you mean that the garage shares a party wall with you? - otherwise I don't understand what you mean.
Unless he has actually built over your boundary, there isn't much can be done on that aspect.
I had the same problem in my flat, the people at the back of me applied to have an extension and I was sent a form from the planning office asking for my objections (if any). I objected on the grounds of diminished light, and lack of privacy as the upper part of the extension overlooked into my kitchen and took away light from my bathroom and kitchen. My objections were denied and the extension went ahead. Until I moved I had the pleasure of the 'hairy' goat of a neighbour leering in at me in my kitchen and having to use lights during the daytime. I do sympathise.