Steven Harper, 38, left Scotland last year to cycle to India and kept in touch with family and friends throughout his adventure.

However, he has now gone radio silent after he foraged, boiled and ate mushrooms near Monaco.

In a message sent to his sister-in-law on 23 November, Steven said: "I ate some mushrooms that you shouldn't eat last night.

"I'm still here to tell you I made it and I'm still alive. It was [tough] and my body was in a state of poisoning, but I live on."

Steven said he was "sure" he'd picked edible mushrooms, but added: "I just had to vomit it up when I woke [because] I could feel that I'd eaten something I shouldn't have."

Steven, who taught English as a foreign language online, last uploaded pictures to his Facebook page on 22 November.

His family said the last post was "geotagged" to a hilltop overlooking Roquebrune-Cap-Martin between Monaco and Menton in the French Riviera.

His older brother, Dale Harper, flew to Nice in France on Tuesday to head a search and has been attempting to retrace his sibling's last known steps.

Dale, 40, told Sky News that he has already scoured part of the coast from Nice to Sanremo in Italy, and Friday's search will focus on the area between Menton and Ventimiglia in northern Italy.

He believes his brother managed to make it into Italy.

Dale said: "If he did ingest and ultimately survive a potentially lethal dosage of a toxic mushroom, then he is more than likely in a state of debilitation from kidney, liver or other damage.

"We don't know what he ate obviously - and it is speculation - but ultimately that is the most terrifying part.

"We need to know if he is safe or needs medical attention."

Read more from Sky News:
Bodycam footage shows police searching for gunman
'Surreal' for teen to be home after being missing for six years

Dale said all the relevant authorities have been notified and nearby hospitals have been checked "many times".

Messages from friends have reported that Steven was robbed of his phone, bike and passport at the beginning of November.

Dale added that his brother was also attacked in Barcelona in Spain and suffered an injured eye.

The search along the beachfront from Ventimiglia to Bordighera will focus on the abandoned tents and homeless shelter pitches.

Dale said: "There are so many places he could have curled up, but we just don't know what he did.

"Steven and I are no stranger to danger, but what concerns me is the state he may be living in and barely anyone will notice in that part of Italy."

A spokesperson for the Foreign, Commonwealth and Development Office said: "We are supporting the family of a British man and are in contact with the local authorities."