Bushby said: “We are talking with the French coastguard.”
Referencing a 2018 “prefectoral order”, the French Maritime Rescue Coordination Centre confirmed the stipulation.
It said it had referred Bushby’s support team to the Channel and North Sea Maritime Prefecture, which manages the order, for them to consider.
The BBC has contacted the body for a comment.
Who is Karl Bushby and why is he walking around the world?
While Bushby said he still hoped Eurotunnel bosses would have a change of heart, he is beginning to draw up plans for the Channel swim.
“We have secured a support boat for October,” said Bushby. “That’s a big thing. I would expect it to take two or three days to swim across to the UK.”
Bushby is currently in Mexico, where he retreats between stages of his challenge in order to meet visa regulations, rest and plan routes.
“I will be back in Belgium in early September,” he said. “Towards the end of that month, I expect to be in France, preparing for the swim.
“I am not angry it has come to this. I am more disappointed. But things could still change. Walking through the service tunnel is still the preferred option.”
Bushby made clear the swim depends on French authorities and the weather.
“We are talking with the French coastguard and we hope an exception [to the rule] can be made,” he said.
“The weather is also a big factor. For a successful attempt, you need a window of good weather.”
Bushby has tackled other large expanses of water on his adventure.
In 2006, he became the first Briton to walk across the Bering Strait, the treacherous 58-mile frozen sea between North America and Russia. That feat required some swimming.
And in 2024, he completed a 186-mile (300km) swim across the Caspian Sea in order to avoid Russia or Iran amid rising global tension.
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