Four police officers and a member of police staff were injured during a spontaneous anti-austerity protest against the new Tory government at the weekend.
Riot police clashed with frustrated crowds outside Downing Street and at least 17 arrests were made.
A massive protest is planned in London for June 20, when tens of thousands of people are expected to converge on the Bank of England.
It is being organised by The People's Assembly, with transport being provided from locations across the country.
In a message on its website, it tells supporters: 'With the Tories going it alone in government we know exactly what to expect. More nasty, destructive cuts to the things ordinary people care about- the NHS, the welfare state, education and public services.
'We demand an alternative to austerity and to policies that only benefit those at the top.'
The People's Assembly was launched in 2013 and is backed by major trade unions, numerous left-wing campaigning groups, MPs and individuals.