Doctor Who RPG The Time Traveller's Companion - Rules of Play says:

Time flies when you're having fun, but flying through time can present a whole host of problems. Whether accidentally creating paradoxes, upsetting the course of history or trying to Put Things Right, you're going to need to know your way around the Vortex. You need a guide…a companion.

This 240 page hard cover supplement for Doctor Who: Adventures in Time and Space gives more information on Time Lords, temporal mechanics and time machines, including:

• Gallifreyan culture, history and law
• New options for creating and playing Time Lord characters
• More on the physics of Time, temporal phenomena and Time Travel
• Detailed information on the TARDIS, and rules for creating your own Secrets of the Time Lords...