Extinction Rebellion have argued that the £37 million Scotland Yard have spent policing their protests this year was a "bargain".
In an email titled 'Extinction Rebellion UK on policing costs: £37 million for all that we hold dear, bargain!', the group argued that they "felt no choice" but to carry out the protests across London.
"Total silence from the government since Parliament's declaration of an environment and climate emergency in May, against a backdrop of ongoing criminal government inaction on the climate and ecological emergency for the last 30 years, meant that Extinction Rebellion felt no choice but to take to the streets again this October," it read.
The statement continued: "If you want to target the messengers then so be it, but that doesn't change the message that needs to be heard.
WATCH: Extinction Rebellion protesters block London's Oxford Circus
"Perhaps this government should look at how they spend money. According to a report by the European Commission in January our government spends £10.5 billion a year subsidising fossil fuels."
Today, Metropolitan Police Commissioner Cressida Dick revealed £21 million was spent on policing a two-week protest carried out by the group over the last two weeks, with a further £16 million spent patrolling an earlier protest in April.
It takes the total spend on Extinction Rebellion in 2019 to £37 million - more than twice the annual budget of the Met's Violent Crime Taskforce, which stands at £15 million.
Dame Cressida said the climate change activism group was now placing a "horrendous strain on London".
Stunts carried out by demonstrators so far in the capital include scaling tube trains, delaying planes from taking off and spraying a government building with fake blood using a disused fire engine.