After five months in a remote jail cell in Greenland, the environmentalist Paul Watson is a free man. Danish authorities arrested Watson in July when he refuelled in Nuuk en route to intercept Japan's new whaling vessel: the Kangei Maru.

Denmark was acting on an Interpol notice requested by the Japanese, who accused the 74-year-old of trespassing, damaging a whaling ship, and injuring a crew member with a stinkbomb in 2010.

Watson found fame as star of the TV show Whale Wars, in which his ragtag navy of activists rammed vessels that were hunting cetaceans. Watson was threatened with extradition to Japan, where he faced 15 years in prison.

But yesterday he was released. Denmark said it had not received sufficient assurances that Watson's five months in jail would be deducted from a potential sentence in Japan. The result is that Watson will be home for Christmas and free to do battle again on the high seas.