I spent the day on a Socialist Party stall near Temple tube on the Embankment.
It was taking contingents two hours to get over Waterloo bridge to the start of the demo, a walk which would normally take ten minutes.
Other Socialist Party members met up with union branches and anti-cuts campaigns at local meeting points in London boroughs or in central London.
The range of people was huge - from seasoned fighters in unions such as the RMT and FBU to middle- aged women health workers on their first ever demonstration; from pre-teens with their families to a man in his 80s who said he had had links with the French Resistance in World War Two.
What they all had in common was that they were marching as trade unionists and anti-cuts campaigners, fighting for their jobs and their services.
Thousands of people made their way from the North West to London.
99% of those on the Unite train who I asked to sign the petition did so.
Two Unite members looking at the leaflet talking to each other summed it up: "A 24-hour public sector general strike - that is what this country needs!" "It needs to bloody wake up!"
"Well, that'd wake them up!"
We distributed up to 3,000 leaflets on the way to London. We sold hundreds of copies of the Socialist, with one Lancashire Socialist Party member selling 75 by the end of the day.
Hundreds of pound coins (or more) rattled into our collecting tins, with many people interested in joining our party.
A couple who were leaving Hyde Park said they'd been listening to Dave Prentis, Unison general secretary.
When asked whether Prentis had said anything about what to do next, their responses were "No, and that's what annoyed me most" and "They need to learn some tactics".
From the Socialist Party at least, a clear message has reached hundreds of thousands of people about the necessary tactics to defeat the Con-Dems and their cuts.
Members of Swansea Socialist Party travelled up on trade union coaches.
The mood on the Unite coach was one of keen anticipation.
At the National Shop Stewards Network rally at Speakers' Corner there were some rousing speeches from NSSN secretary Linda Taaffe and anti-cuts convenor Rob Williams, pointing the way forward for fighting the Con-Dem cuts.
The coach back was enthusiastic and determined. That over 500,000 people had marched without the TUC even pulling out all the stops shows the potential for organising opposition to the cuts.
Louise from Cardiff said it had been her first big march and had given her a boost to keep on campaigning.
"I was surprised at how many people were there. When we were leaving they were still coming in!" she said.
Taxi drivers taking Socialist Party members to Newcastle station were extremely supportive of the demo.
One had said he thought it was great that people were protesting against the government. Our taxi driver, whose wife is a civil servant and whose job is threatened, gave a discount on our taxi fare.
Three coaches from North Devon - mostly new people who haven't been involved in campaigning before, who can now get involved in North Devon Anti-Cuts Alliance.
The main thing about the march that stuck in the mind was the sheer numbers of people there, and the encouragement that most seemed to get from the events.
Brilliant demo. Lots of leaflets handed out, Socialist papers sold and lots of people spoken to about the Socialist Party.
The highlight of the demo was definitely the NSSN rally at Speakers' Corner. Coventry Socialist councillor Dave Nellist's and Peter Taaffe's speeches in particular were very inspiring.
Bring on the 24-hour strike!
In the evening, the demonstrators in Trafalgar Square had created a positive and relaxed atmosphere.
Lots of people were sat on the floor or dancing to music played by a samba band, while children slept in prams.
Suddenly around 500 police in riot gear charged into the crowd. They created a small circle and faced outwards, slowly made the circle bigger by violently pushing people and using their shields to hit people.
This intrusion had an instant effect on people's behaviour, who started to panic. Some people reacted by pushing back against the violent behaviour while others pleaded with the police to stop.
Police pushed a group of people, who were standing on railings to the floor and kicked people who where sat down. The picture of a violent group of protesters painted by the media was a complete lie and proof that their reporting can never be trusted.
The RMT transport workers' union had a contingent of around 2,000 members from all over Britain.
Members from nearby stations came over to our RMT delegation and offered their support.
'The cuts kill, kill the cuts' t-shirts were handed out, along with special flags and sticks of rock.
The RMT delegation marched off with its own brass band at the front. It was a lively delegation and its huge turnout was in a buoyant mood.
We sold around 25 papers and hundreds of the Red Line newsletter were taken by the delegation. Many signed up to become members or find out more about the Trade Unionist and Socialist Coalition (see page 11).
It took Lewisham NUT five and a half hours to finally reach Hyde Park. We saw Birmingham NUT finally make it at 5pm - six hours after the start.
The last march of this size was the mass demonstration against the Iraq war - but this demo was different. It was a trade union called event packed with thousands of trade union banners and flags.
Now the urgent task is to harness the power of the movement - into coordinated strike action against the cuts to pensions, jobs and services!
7.05 Outside Newport train station.
Unison members arriving with a smattering from other unions. A feeling of expectancy and excitement.
7.55 On the motorway. One old worker at the back of a West Country bus gives us a clenched fist salute. Demo coaches form an informal convoy gathering strength as we chug through the Wiltshire countryside.
8.50 Dozens of coaches stacked up at Membury services. The Socialist is selling faster than the overpriced hotcakes! One woman caught her bus from Ceredigion at 4am.
10.40 As our bus comes into London there are more coaches with placards.
"Banksters to blame," declares a handwritten Unison placard. Socialist Party leaflets calling for a 24-hour general strike are spread over the windows of a bus from Bristol.
11.10 At last we arrive at the New Covent Garden market coach park.
There are no stewards or directions so we guess the way towards the demo.
Along the way cars are tooting their support. It's becoming a march in itself as we merge with other demonstrators.
12noon We get to Westminster Bridge as Big Ben strikes twelve, but we can hardly hear it as thousands cram onto the bridge waiting to get onto the demo. There is a growing sense of excitement as people realise just how big the demo is.