Rule Britannia - Daphne du Maurier

Emma wakes up one morning to an apocalyptic world. The cozy existence she shares with her grandmother, an eccentric retired actress known to all as Madam, has been shattered: there's no post, no telephone, no radio - and an American warship sits in the harbor.
As the two women piece together clues about the 'friendly' military occupation on their doorstep, family, friends and neighbours gather round to protect their heritage. In this chilling novel of the future, Daphne du Maurier explores the implications of a political, economic and military alliance between Britain and the United States.
"A diverse and engrossing cast of characters...provocative, diverting."- Chicago Tribune