Competition commission - replaced the Monopolies and Mergers Commission on 1 April 1999. It conducts inquiries into monopolies, mergers and the regulation of utility companies, and hears appeals concerning infringements of the Competition Act 1998. Its coverage includes retail and the food chain.
FT.com - market data section; quotes of around 3,000 equities traded on the London market; also companies traded on other exchanges. End of day prices for 8,000 shares worldwide. Subscriber sections (marked with R in blue circle) are only accessible on campus.
BigCharts - has UK stocks going back 10 years. If you use the Java chart option you can get a closing price for any day of the period by clicking on the chart. You can also compare the stock's performance against major indices