https://en.wikipedia.org/wiki/The_Great_War_in_England_in_1897The Great War in England in 1897 was written by William Le Queux and published in 1894.
Le Queux's work is an early example of Invasion literature genre, which began with The Battle of Dorking in 1871, where the British are soundly defeated by an invading German army. The Battle of Dorking was written by army veteran George Tomkyns Chesney, originally as a warning against the further demobilisation of the British armed forces.
It was first serialised in the weekly paper Answers. It was a huge success, and after being published as a book, it went through eight editions.
Le Queux's novel depicts Britain being invaded by coalition forces led by France and Russia, who make several early advances, but the brave English patriots fight on and eventually manage to turn the tide, especially after Germany enters the war on the side of the British.
By the end of the story, the invasion goes the other way as the victors divide the spoils: Britain seizes Algeria and Russian Central Asia, thus decisively winning The Great Game, and Germany annexes more of mainland France in addition to Alsace-Lorraine, thus leaving the enemies crushed and both the British and German empires the dominant forces of Europe.
https://archive.org/details/greatwarinengla00queugoog