Type 400 was a variant of TARDIS developed by the Time Lords and more advanced than the earlier Type 40 model and the models used by other renegades. It was developed at some point during the Seventh Doctor's time.
Coordinator Narvin used a Type 400 TARDIS on a mission for the Celestial Intervention Agency, considering it "top of the range" compared to the "scrap" the Doctor used. However, he lost the TARDIS. (AUDIO: The Quantum Possibility Engine)