A Foreign Office spokesman in London said:"We are supporting the family of a British national who has been hospitalised in Thailand."
It was later disclosed that three days earlier Mr Clarke had posted a selfie of himself hanging out of a carriage window.
He was found unconscious by the tracks this morning wearing the same blue vest as when he took the picture.
It is not known how long Daniel had been on the train and where he boarded it before falling off.
He was noticed by a train driver this morning, who told local police and rescuers he believed Daniel had fallen from the train in front.
The friend pictured in the selfie with Daniel, Ross Wild, confirmed that he had now found Daniel but declined to comment further.
Meanwhile, doctors said that Daniel is being treated at the Chumphon Khet Udomsakdi Hospital.
Dr Sanchai Nakaphan said surgeons had operated on Daniel and scans showed he had not suffered brain damage.
