Thousands of protesters from around the country have descended on London, to march under the slogan "No more lies, no more war".
The Stop the War Coalition, who organised of the demonstration, say they want to draw Labour's attention to their concerns over the situation in Iraq, ahead of the party's annual conference.
This is the fifth protest this year against Britain's intervention in Iraq.
Do you think the protests make a difference? Are you involved in the march? Tell us your views and experiences.
This debate is now closed. The following comments reflect the balance of views we received.
I believe that it would be entirely wrong to remove our troops for Iraq. Regardless of whether you agree with the reasons for going to war or you believe you have been lied to, the fact remains that the troops are there and if they weren't, anarchy would reign and we could end up with something much worse than we had before with Saddam.
It isn't too late to demonstrate. It is too late to stop this war, but if Blair can be held accountable and prosecuted for this war then he might not be around to start the next.
I am tired of hearing people say thousands of Iraqis are dying. It's simply not true! Under Saddam that was true, and if they weren't killed they lost hands, or their homes, or jobs. The fact is most of the Iraqi's support us there, because they know what we are bringing. What changed in the West so that we no longer can take a moral stand against evil?
Josh Ehrich, USA
I have just come back from the London Stop the War march. The numbers disgracefully under-reported as usual! Even a cursory analysis of the kinds of people who took part in large numbers today and on previous demonstrations reveals their diversity. We come from all parts of society, mostly non-affiliated politically, but all united in opposition to a corrupt war and to those who lied to bring us into it.
Would today's protesters really prefer that Saddam Hussein were still in power? How do they explain the surveys that show the majority of Iraqis are pleased the war took place? OK, so they dislike Blair but they should not let that could their judgement.
Michael Liebreich, UK
As someone who was for the overthrow of Saddam I am pleased to see this demonstration, it illustrates what the war was all about - freedom and democracy. The people of Iraq are now able to exercise their own protests, something they could not do under Saddam.
gary gatter, UK
Why don't people stop taking the 'moral high ground' and assess the reality of the situation? So what do they propose if all the forces leave? Will there be a self-propelling society creating jobs, rebuilding infrastructure, upholding the law? They accuse the forces of not thinking of the consequences, yet they appear to be doing just that. I suggest they provide solutions, not criticisms.
If the march achieves nothing else, it reasures those of us who despair that the UK population is becoming a nation of sheep prepared to bow down to political lies and spin.
N Hawkins, UK
If the anti-war groups really cared about Iraqis then they would spend more of their time and resources organising charity events and raising funds for those who suffer from the effects of all wars.
I would have been involved but I don't like the fact that this march had two different protest aims. Yes, I am 100% against the War in Iraq. No, I cannot march in support of the Palestinians. The two issues are separate and should not be merged together for the purposes of this march.
Protests can make a difference, but sheer numbers indicate strength of feeling, not strength of argument. And the argument - that troops should leave Iraq - is an absurd one.
Yes they do make a difference. It about time the truth come out. Thousands of Iraqis are dying which does not make the Headline News but as soon as Coalition member get killed it become Headline news everywhere.
Julian Opoku, USA
Pity the protesters didn't go to Iraq before the war and demonstrate against Saddam's regime.
The protests won't make any difference, but they are very important. The government needs to realise that the population is very unhappy about being so consistently lied to. We aren't as stupid and gullible as the government thinks. I think the press should highlight the fact that at least 20,000 Iraqis have died, many thousands of those being children. Tony Blair has lied to us about WMD and now has the blood of many innocent people on his hands. He must resign.
Having come back from the start of the march, where I spoke from my platform at Speaker's corner, I want to re-iterate the points I made:
a) The march is pointless. Its aim, of pulling US and UK troops out does not address the cause of the war - capitalism's need for resources to exploit. If America pulls out, Iraq will end up in the hands of yet more Capitalist gangsters, either by arrangement or bloody civil war.
b) Marching is pointless because real power lies in the hands of capitalist politicians, who the people on the march voted for. So long as politicians who support capitalism are in power, they will pursue war strategies. Not in your name? You voted for it. Only concerted political action to abolish capitalism and usher in world socialism will solve the problems of Iraq and the whole world.
Bill Martin, UK
Aren't people glad that Iraq is now free to develop as a free and potentially very prosperous nation? War is never nice but in the long run it is the right thing to have done. Saddam is one less mad dictator to worry about.
I don't think the protests really matter anymore. I mean do any of the participants really expect the UK to withdraw it troops? If so, why? The troops in Iraq are doing their job, and these protests simply make their job harder. In the US I have been to pro-US soldier rallies, perhaps those could be done over here as well.
Tim Ibisch, USA
Whether or not you agreed with the war in Iraq, we all must join together to help the people there now. Every country around the globe should be lending a helping hand. The only people who are really going to suffer from lack of help are the Iraqis. Leaders from neighbouring Arab countries need to do more to help as well. Pulling troops out now would only allow Saddam Hussein's regime to regain power and start to ruthlessly kill thousands of innocent people. There is no going back now.
E. Tomasson, Iceland