The UK embassy in Moscow has complained to the Russian foreign ministry about harassment of Britain's ambassador by a youth group with links to the Kremlin.
Mr Brenton complained of harassment by Nashi activists
The embassy told the BBC that Russian officials pledged to investigate.
Members of Nashi, which supports President Vladimir Putin, objected to Ambassador Anthony Brenton's attendance at an opposition conference in July.
"We are picketing the residence of the ambassador," said Vladimir Katasonov, a Nashi spokesman.
"One of our activists is staying every day there," he told the BBC's World At One programme.
Mr Brenton attended an opposition conference called Another Russia on 11-12 July, which was billed as an alternative to the G8 summit in St Petersburg.
Among the opposition activists there was Eduard Limonov, leader of the National Bolsheviks - regarded by Nashi as a fascist organisation.
Mr Katasonov said Nashi wanted Mr Brenton to apologise for having shown support for the opposition groups.
Nashi, which says it is working to combat fascism in Russia, was launched in April 2005. It claims to have thousands of followers.
Another of its stated goals is to thwart any pro-Western mass movements of the kind which took power in Georgia and Ukraine in recent years.
The British protest comes amid strained relations between Russia and the UK over the poisoning of former Russian spy Alexander Litvinenko in London.