There are thousands of hospitals in the UK. Every major town and city has a least one hospital and a doctors surgery or clinic. To find london hospital addresses, there are various resources that you can use online.
The fastest is to just go to a page like this one: london hospital addresses, which contains a list of hospitals in London with addresses and other contact details.
Another method is to use the NHS website and find the list from their hospitals directory. This is the best UK hospitals directory for NHS hospital and it's available from the NHS website.
You can also find london hospital addresses by using the local pages of a search engine. Every major search engine like Google, Yahoo and MSN has local pages that you can use to locate and find addresses of any organization by town, city or region. It's a wonderful free resource that you can use anytime. All you need is an internet connection.
Of course you can use tradition resources such as the Yellow Pages or your phone book. Remember, many of the companies that publish these types of directories also have websites where you can lookup organizations online. I think the yellow pages have a site called yell.com but I'm not too sure.