The Office of Fair Trading has published a report about the law as it applies to the sale of residential property using internet websites.
According to the OFT, if you operate a business that accepts instructions from clients wishing to sell their homes, then if you either 1) do things to effect an introduction to your client or 2) after making an introduction, do things to secure the sale or purchase of the property, then you are legally an "estate agent" and must therefore comply with the terms of the Act. It seems the only exemption is if you are merely "publishing advertisements or disseminating information".
