Shadow government

A Shadow Government is a secret "government in waiting" that remains hidden with the intent to take control of the government should a crippling catastrophe occur.

United States:

• Continuity of Operations Plan and
• Presidential line of succession

United Kingdom:

• The Civil Contingencies Secretariat is responsible for planning for government continuity in the event of catastrophe, although it is not itself a "shadow government"

For alternate topics of government check out Governmental Questions