The RNIB certainly can assist. Remember websites should not be designed for visually impaired users because it is helping them ... it is ... and it is nice to do so, but it is also the law. There are legal implications. Trying looking at screenreader.net who provide some information that you might find useful. Also, userdesign.co.uk who have various pages related to design but do focus on web design especially listing other useful websites for you.
I hope this helps you and many others.