Must be a strong swimmer too. England to France?
What is the timeline? Is you character fighting off Muslim hordes.
Time would help. I have been a backpacke nearly my entire life. Gear, shows, backpacks, name brands will make it believable. The Tyrole hills should be mentioned. Matterhorn. In England you have the royal walking trails that must remain open through any proprty. Lots of sheep to see.
What I have heard is hitching from England to France without swimming is definitely possible. Challenging, and a bit dangerous, as hitchhiking always is. But possible. A preplanned ride with a commuter doing the channel tunnel, taking up with a trucker, and finessing a car-less ride on one of the ferries at Dover have all been suggested by various online hitchhiking guides. Disclaimer: I am not recommending any of this. It’s simply something my story’s character is driven by circumstances to attempt.
As for timeline, it’s contemporary, so yes, encounters with Muslims and other populations in movement are possible. But not certain. Even large movements can be harder to see close up.
But thanks for the tips. They all look useful. The royal walking trails? Oh my. :)