You won't get very far in British Rail Blue or InterCity eras without the official font, so here it is in two versions: British Rail Light Normal, and British Rail Dark Normal. As far as I can see, the 'light' was for use on pale backgrounds and 'dark' (which is slightly bolder) was used for dark backgrounds such as Corporate Blue.
The font set isn't just letters and numbers: it also includes the full set of characters such as the BR double arrow logo and all the signage characters such as exit arrows for station signage, timetable symbols and so on.
Enjoy!
Paul