John Apter, national chairman of the Police Federation of England and Wales, tweeted: "These officers are just doing a job, they're somebody's son, daughter they're mums and dads".
They said that demonstrators at the protests threw missiles, including bottles, at the officers. Two policemen eventually had to go to hospital, but they were not seriously injured, police said. "We wish all our injured colleagues a swift recovery and will be supporting them as best as we can".
The authority added that five people were arrested for offenses, including assault on police.
Several thousand anti-lockdown demonstrators have marched through central London despite restrictions on mass gatherings during the Covid-19 pandemic.
Police respond to the mass gathering as things turned ugly
Non-essential shops and outdoor hospitality reopened on April 12, but indoor gatherings are still banned until May 17 at the earliest.
Thousands of people protested today in St.Gallen in eastern Switzerland against measures by the Swiss government to curb the virus.
Demonstrators protested against the Covid-19 lockdown restrictions and the prospect of vaccine passports.
England's latest Covid-19 lockdown measures have been in place since early January, after the United Kingdom saw a surge in cases.
Months of restrictions alongside the successful vaccine rollout - with more than 45 million doses administered - has seen the situation improve.
Britain has been among the hardest hit in Europe by Covid-19, recording more than 127,000 deaths within 28 days of a positive test.
Ontario worship services limited to 10 again as COVID surges
Ottawa has also shipped more equipment such as oxygen units and drugs to treat COVID-19, he said. Ontario is controlling what it can control, he added: "Air travel is under federal jurisdiction".