Insulate Britain, a new group whose campaigners have repeatedly blocked roads and motorways in and around the capital, targeted three locations including the Canary Wharf and City of London financial districts.
The activists, who want the government to insulate all British homes starting with social housing, began their disruptive demonstrations last month but temporarily suspended them in mid-October to give themselves and the public "a break".
The restart of their protests, which have infuriated drivers and led to some confrontations, comes as the UK prepares to host the UN COP26 climate summit in the Scottish city Glasgow later this week.
"3 locations across the city of London are currently blocked by #InsulateBritain," the group said on Twitter.
"We demand a meaningful statement that the government shall insulate the UK housing stock," it added.
"Why should we wait until millions have lost their homes, are fighting for water or starving to death?"
Police, which responded to Monday's renewed protests, have arrested hundreds of Insulate Britain activists -- with some people detained several times -- since they began the demonstrations on September 13.
The government has meanwhile secured court injunctions leaving activists facing court summons and possible imprisonment or an unlimited fine if they block some motorways.
But the group, which has demanded ministers produce within four months a legally-binding and funded national plan to retrofit all homes by 2030, has vowed to continue its campaign.
The government last week outlined more detailed plans to reach net-zero carbon emissions by 2050, but was accused by climate campaigners of lacking the necessary ambition in many areas -- including home insulation.