Jeremy Corbyn is to launch a staunch defence of the Stop the War Coalition in the face of criticism from senior figures in his own party.
The defiant Labour leader will insist the protest group is one of the most important campaigning organisations of modern times and say that attempts to close it down are anti-democratic.
Mr Corbyn, who chaired the movement before taking charge of the party in September, is attending its fundraising dinner in London despite calls from a number of MPs, including former frontbenchers Tristram Hunt and Caroline Flint, to shun the event in the wake of a series of controversial statements about terrorism and air strikes on Syria.
A tweet and article published following the attacks on Paris suggested France had ''reaped the whirlwind'' of Western support for extremist violence in the Middle East.
Mr Corbyn will tell campaigners at the dinner: "The Stop the War Coalition has been one of the most important democratic campaigns of modern times.
"It has brought hundreds of thousands of people on to the streets time and again. It has organised protests and lobbies in every part of the country, including by military families.
"Most of all, it has been shown to be right in opposing more than a decade of disastrous wars - in Afghanistan, Iraq and Libya - while many of its most vociferous critics supported them.
"The anti-war movement has been a vital force at the heart of our democracy. Branding it as somehow illegitimate is an attempt to close down democratic debate and campaigning."