Vladimir Putin owns an undeclared villa complex on a scenic island near the Finnish border where a Soviet version of Sherlock Holmes was filmed, according to two investigations.

Mr Putin is the owner of the Sellgren Villa on Lodochny Island in the Bay of Vyborg, a red brick home built in 1913 and recently expanded, separate investigations by the independent online channel TV Rain and Alexei Navalny, the opposition leader, have discovered.

A drone flyover of the expansive property by Mr Navalny's Anti-Corruption Foundation showed a new 1500 square metre wing on the villa, a helipad, a pier, a guesthouse built in the same style, and a large house and garage, presumably for staff.

The villa is not mentioned in the president's 2016 income and property declaration, which said he owns a 1500 sq m land plot, two cramped flats, three Soviet-era cars and a small cargo trailer. Mr Putin has previously been linked to a palace on the Black Sea.

"This is very real corruption. This is the luxurious life of the head of state, paid for by money stolen from us, and this is the reason for poverty," Mr Navalny said in a YouTube video about the investigation that got more than 1.8 million views in 24 hours.

He called on supporters to demand he be allowed into next year's presidential election despite a controversial embezzlement conviction that the authorities said would bar him from running.

The villa was designed by Uno Ullberg, a Finnish architect, and served as the home of Von Bork, a German spy in a Soviet-era version of a Sherlock Holmes film.