The local authority will have a local plan and presumably the proposed building falls within this plan, you do not say if the LA have granted planning consent to the builder but if they have not it is not unreasonable to assume the builder would appeal against any adverse decision made and many appeals are successful with or without variation.
You ask what you can do and Kristal has made some sensible suggestions particularly if there are bats or other protected species that would be disturbed by this development you should contact the appropriate organisation. You have the right to light if your windows have been illuminated for the past 20 years and the proposed house would stop this, permission must be obtained. It will also be helpful if you can organise others who may be affected by this development to make their complaints in writing.