Page 276. " waiting for its bomb "
by cm

7/7 Memorial
Creative Commons Attribution Share Alike7/7 Memorial - Credit: Romazur, Wikimedia
It would come sooner than expected.  Saturday was published in January 2005.  On 7 July of the same year, four bombs were exploded within minutes of each other at different points on London's public transport system: three Underground trains and one bus.  The bombers, all of whom died in the attacks, were British muslims motivated by the UK-US invasion of Iraq.

52 other people were killed and around 700 injured.

Page 276. " what was their body count, Hitler, Stalin, Mao? "

Belsen, 1945
Public DomainBelsen, 1945 - Credit: Lieutenant Alan Moore
Perowne's estimate is probably on the low side:

Adolf Hitler could be said to be responsible for World War II, in which around 60 million people were killed, including up to 25 million military dead and 6 million Jews systematically murdered on Hitler's orders.

Joseph Stalin ordered the execution of close to a million people, and the deportation of many more to the Gulags where around 2 million died.  Some historians estimate much higher figures.  Some also blame Stalin for the 1932-33 famine, which killed 6-8 million people.

Mao Zedong led China through a series of political and social programs, including the Great Leap Forward and the Cultural Revolution, which caused the deaths of as many as 70 million people through famine and starvation.