If you live in a listed building, conservation area or your house has a restrictive covenant, you'll need to follow certain guidelines to ensure your new windows are "in-keeping" with the surrounding area.
Houses in conservation areas are subject to 'Article 4 Directions', which restrict the work that you can do to the outside of your property, without first getting planning permission. If this is the case, it’s often simpler to find a company with previous experience of getting windows accepted in conservation areas. Ask your window company for details of previous projects that have been accepted by Planning Officers.
Other than these legal necessities, it’s up to you what style, colour and glass designs you want for your windows!