I reckon you'd do well to start with Wikipedia. Type in 'British Railways' and you'll get more info than you need on the chequered history of BR, which I suspect you don't want; but look further down the page and you'll see a section on 'Successor companies'. Here you'll find more relevant data about the modern scene, and by following the links you'll discover other pages giving details of rolling stock and other interesting stuff. You'll soon find yourself engrossed in it all. Enjoy!!
