'Letter of last resort': Theresa May's first job as prime minister will be to decide on UK's response to nuclear attack
It's a moment when a new prime minister truly realises the power and responsibility he/she holds.
One of Theresa May's first tasks when she enters Downing Street later is to write "a letter of last resort".
This is a note sent to commanders of Trident submarines which outlines what should be done if Britain is attacked, or even wiped out, by a nuclear attack.
The commanders, presuming May is dead or uncontactable, will be required to follow her strict instructions - which may be to fire a nuclear missile in retaliation.
David Cameron's note will already have been destroyed by the time May writes her.
Tony Blair went very quiet and pale when writing his, according to onlookers.
Scary stuff.