Vladimir Putin, the Russian president, has been linked to ownership of a villa complex on a scenic island near the Finnish border where a Soviet version of Sherlock Holmes was filmed, according to two investigations.

It is claimed in a YouTube video, which got more than 1.8 million views in 24 hours, that 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, according to separate investigations by the independent online channel TV Rain and opposition leader Alexei Navalny.

A drone flyover of the expansive property by Mr Navalny's Anti-Corruption Foundation showed a new 1,500-square-metre wing on the villa, a helipad, a pier, a guest house 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 1,500-square-metre land plot, two cramped flats, three Soviet-era cars and a small cargo trailer. Mr Putin has previously been tied to a palace on the Black Sea.