The group confirmed in a statement that around 50 of its members have blocked four major routes, including the Blackwall Tunnel under the Thames River in East London, Hanger Lane and Arnos Grove, in the northern part of the city, and Wandsworth Bridge, in South London.
In previous weeks, the group focused mainly on the M25, M1, and M4, three busy highways around London, and the Port of Dover, in southern England, but on Sunday the government got a fresh legal injunction banning protesters from the Strategic Road Network linked to the M25 in the southeast.
"This new injunction covering the Strategic Road Network in and around London is another step forward in helping to keep these reckless and dangerous protests away from our network and endangering peoples' lives", National Highways Regional Director Nicola Bell said in a statement.
Transport Secretary Grant Shapps also warned on Twitter that the government would introduce new laws to send perpetrators to jail for up to six months and impose unlimited fines on them.
"We will not stand by while motorists are held hostage", he added.
Hundreds of climate activists have already been arrested and later released from custody since the protest action began, but some of them may face a court hearing and imprisonment or a fine for contempt of court if they are found to be in breach of the injunctions going forward.
Insulate Britain, which claims that the £1.3 billion ($1.7 billion) announced by the government is only 0.2% of what is needed to properly insulate the 29 million homes in the UK, has said that 8,500 deaths in an average UK winter are a result of cold homes and that thousands of families "have to choose between heating and eating".