The link below will take you to FAME, an online database that provides UK company financial data. This data is extrapolated from various sources including the company's own accounts submitted to Companies House and published in their annual reports. The benefit of using this is that you will be able to view data from a ten year period, allowing you to spot trends over a longer period of time.
You will need your SIngle Sign On username and password to access this database.
The following websites give you varying degrees of financial data:
Companies House, the UK equivalent of the SEC in the USA, collect key company documents such as accounts and an annual return containing details of directors. Such details must be submitted to Companies House who then make the information available to the public. There is also an interesting section on the formal and legal procedures for setting up and running a UK company.
Morningstar contains data, news and research on shares and funds, unique commentary and independent research on a broad range of investments. The site is particularly useful for international companies giving stock prices from a range of Exchanges as well as key financial data.
In the USA all companies are legally required to file registration statements, periodic reports, and other forms electronically through EDGAR, part of the Securities and Exchange Commission (SEC). This information is freely accessible and can be downloaded for free. There is a simple search facility and brief tutorial to help you find the information you need.
Finding out whether the company you're researching is solvent, if they making a profit and what their turnover is can be a useful source of information.