Thousands of police officers are expected to join a protest march against cuts to public services today.
Organisers said they hoped 20,000 officers would march through central London, with 16,000 wearing black caps to signify the number of expected job cuts.
Union leaders said up to 400,000 civil servants, lecturers, health workers, Ministry of Defence staff, immigration officers and members of the Royal Fleet Auxiliary would join demonstrations.
Police refused to rule out kettling officers who take part in the march. Making clear that the Met Police intended to treat the demonstration like any other, a spokesman said: "There will be an appropriate policing plan in place to deal with the march."
Paul McKeever, chairman of the Police Federation, said: "The march is the only way that police officers can demonstrate their anger. The reality of the cuts to policing is really beginning to bite; numbers are beginning to fall rapidly."