Police Federation warns that its members are closer to joining the marchers as anger grows over planned cuts to pay and conditions

A deepening antipathy for the government's public spending cuts has been revealed as the head of the police union said officers patrolling next weekend's demonstrations against austerity measures would have "a lot of sympathy" with the protesters.

Emphasising the growing opposition to the speed and breadth of the cuts programme, the chairman of the Police Federation, Paul McKeever, said that officers on duty at Saturday's March for an Alternative in central London would be feeling a sense of solidarity as they policed the event, which is being organised by the Trades Union Congress (TUC).

"The great irony is that officers policing marches like the TUC are actually facing greater detriment than many of those protesting against the cuts," said McKeever, whose union represents 140,000 rank-and-file police officers.

"We're not members of the TUC and have to be careful about having too close an association, though there will be a lot of sympathy towards those marching."

The march, due to be held in London's Hyde Park, looks set to be the largest rally to date against the coalition government's policies, with organisers hoping for more than 100,000 people to attend.

Along with the unions and other campaigning bodies, a plethora of other protest groups has sprung up as the strength of feeling grows against a package of issues as diverse as tuition fee rises, the scrapping of the education maintenance allowance, bankers' bonuses, tax evasion by big business, library closures and arts and public spending cuts.

One peace activist, and veteran of the anti-war marches in 2003, told the Observer: "We will get a lot of first-time protesters on Saturday because people are getting more confident that protest is for them. It's not for a bunch of anarchists, it's families, students, old people, maybe now even the odd police officer, who don't want to put up with cuts and unfairness in Britain any more."

Groups are using technology and social media to share expertise and information as well as co-ordinate and manage direct action more efficiently. The day is expected to see traditional protests take place at the same time, with sit-ins at high street shops and banks and occupations of public buildings and universities.

In the past five months, the protest group UK Uncut has staged a steady campaign of sit-ins against tax dodging that have forced the temporary closure of branches of Barclays, Vodaphone, Boots, British Home Stores and Topshop up and down the country.

"26 March is going to be a really important day," said Anna Walker of UK Uncut. "We had the student protests and we have seen the growth of UK Uncut, but this is the first time we are going to have people from all over the UK together whose lives are being turned upside down by these cuts. It is going to be the start of something powerful."

Scotland Yard has already suggested that "troublemakers" could attempt to hijack the protest. The Met was criticised for its tactics at student tuition fee protests last year, when dozens of people were arrested during violent outbreaks. This time, members the of human rights organisation Liberty will act as independent observers.

McKeever suggested that, far from being hostile to the protesters, many police officers would share the frustrations of the day. He said that a massive march of police officers themselves could not be ruled out if the home secretary, Theresa May, pushes forward with government plans to cut back on police pay and perks.

More than 20,000 police officers marched through London in 2008 in protest about their pay, the biggest demonstration in police history.

"We had 23,000 officers on the streets on a point of principle. Imagine how many might be involved with the level of feeling at the moment. Nothing is ruled out," said McKeever.

He also warned that attempts by the government to force through changes in pay and conditions might lead to legal action. "We are exploring every avenue to make sure officers are treated fairly.

"The first duty of any government is the protection of its citizens. Yet it is being vindictive against a police service it seems to hold in very low regard.

"Mervyn King has said that it's not those in the public sector who are to blame for the crisis, but it doesn't feel like that in the police service."

He added: "They don't seem to be so accusatory towards those where the blame actually lies. There seems to be a dislike of policing with this present government – the so-called party of law and order is dead, it's buried, it's gone."