Rallies were held at all six regional offices including the CSA's London headquarters in Millbank, Westminster. In Leeds, West Yorkshire, about 500 absent fathers and their partners marched through the city centre, bringing traffic to a standstill.
In Plymouth, Devon, police and security men kept protesters away from the CSA building where a 200-strong crowd jeered at staff arriving for work.
About 300 demonstrators gathered outside the agency's Midlands Regional office at Brierley Hill, West Midlands. The crowd began arriving at 7am and hurled abuse as staff arrived for work. A wreath was laid at the foot of steps outside the office in memory of the fathers who, it was claimed, have been driven to suicide by the agency's demands.
In Bury, Lancashire, the home of Alistair Burt, Under-Secretary of State at the Department of Social Security, was found to be daubed with the slogan 'Women and Men say 'No' to Peter Lilley's Gestapo'.
The words in green luminous paint on Mr Burt's garden wall were discovered by a passing police patrol and inquiries were taking place to find the culprits, a spokeswoman for Greater Manchester Police said.
Didi Rossi, a member of the Campaign Against the Child Support Act, one of the main protest groups, said: 'We have many supporters all over the country. This Act affects women just as it does men.' Asked whether she approved of this action, Ms Rossi replied: 'People are very angry about what is going on. Single mothers have been persecuted from the start, even before this Act came in. This shows that people are really furious.'
She was asked whether she thought that yesterday's action helped their campaign, and replied: 'I believe it does. Because it gives publicity to our cause.'
Meanwhile, Mr Burt admitted it had been a difficult year for the CSA. He said: 'There are a proportion of people who have not paid maintenance, who don't want to pay maintenance and who make life difficult for their first families.
'All too often the balance of this thing is very much the other way. It is important to hear that voice.'
And he warned that men who deny paternity of children to avoid the attentions of the agency - as the Independent revealed on Monday - were running up a larger bill for themselves, as this was an issue dealt with by the courts.
'There is no loophole. The courts previously dealt with paternity and they still do. The Child Support Agency was never intended to deal with that,' Mr Burt told the Today programme on BBC Radio 4.
Ros Hepplewhite, the CSA's chief executive, claimed that 99 per cent of people were happy with the agency and complaint levels were running at less than 1 per cent.
She told BBC Radio 5 Live: 'I don't think there is a tremendous sense of hostility to the new arrangements.'
This claim was denied by a spokesman for the Campaign for Fair Maintenance, which has a network of almost 200 groups around the country and claims to have been contacted by 100,000 people unhappy with the CSA's demands.
Yesterday the pressure group Gingerbread, representing lone parents the agency is supposed to help, joined in the attack.
Mary Honeyball, chief executive, said: 'The current system is not working because people do not perceive it to be fair. People see the Treasury benefiting but not their own family. Most families are currently no better off after the intervention of the CSA. The rigidity of the CSA - which has no element of discretion - has also led to bad decisions that have wrecked lives.'
Donald Dewar, Labour's social security spokesman, said there was little cause for celebration on the CSA's first anniversary.
'It has brought dismay, anger and despair to many,' he said. 'The Government has tinkered with the financial formula but has totally failed to introduce the kind of radical change that is required.
'What Labour wants is radical reforms to inject justice into the system. Without early action, the potential for unhappiness and discontent is awesome.'
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