Too late. We already have been invaded. Only this time not by any military force.
Mines: shut and flooded (impervious to aerial bombing)
Steelworks: all bar a few torn down (lot of acreage, requires lots of bombs)
One-trade towns: downsized, jobs sent to China, population put on benefits
Forests: intact, give or take a tiny amount of clearance to make grouse moors in England, before the border closes
Tourist sites: unharmed
Privileged elite: showing no fear of threat
Farmers: working at peak efficiency
German cars: commonplace
Energy suppliers: no damage. Growing, in fact
Golf courses: increasing in number
City financiers: thriving
Unlike the Norman invasion, however, it is not entirely clear who the replacement elite are. Still big on heraldry err, I mean logos.
Would I fight for my country? I don't know. Some countries seem to be lapdogs to far the more powerful multi-nationals. I might consider being a mercenary but I wouldn't last more than 30 seconds against the video-game generation.