The Doctor:  Fascinating history , Downing Street . 2000 years ago , this was marshland . 1730 , it was occupied by a Mister Chicken - he was a nice man - 1796 , this was the Cabinet Room . If the Cabinet was in session , and in danger , these were about the four safest walls in the whole of Great Britain . End of Lesson .
The Doctor: Installed
The Doctor: in _ 1991 _ , 3 inches of steel lining every single wall . They 'll never get in .
Rose Tyler: But how do we get out ?
The Doctor: Ah .