After the Mark 1 there were various improvements to the basic model, such as the Mark 2, but the Mark 2s had thinner armor alongside the Mark 3, and were deployed with overconfidence by the British military. The Mark 2 was used mostly for training purposes, only 50 were built.
But on a personal note: Who in their right mind would put the fuel storage of an armored vehicle in the FRONT, where they would be shot at the most? And why were the escape hatches so difficult access?
Video lecture courtesy of David Fletcher of the Bovington Tank Museum.