These organisations provide useful information and advise if you are starting in business
The British Library run a wiki called Business Essentials on the Web. This wiki lists many resource websites helpful to small businesses. It should save you time searching the web. Within this wiki you will find a list of Enterprise Agencies in London. Included in this list are a number of private and commercial organisations operating in the enterprise sector in addition to the not-for-profit registered enterprise agencies
The City of London publishes a list of sources relating to accessing finance
London Small Business Centre is an Enterprise Agency providing funding, workspaces, training, business Advice and Mentoring to small business startups
South East Enterprise is a not-for-profit registered enterprise agency providing support for start up businesses in South East London
Startups is a commercial resource if you are starting and growing a business. The site lists a number of reasons specifically for starting a business in south london
This web site is not endorsing any organisation and it is up to you to make your own judgement