“During the campaign there was a deliberate tactic by the Leave camp to create alarm among elements of the population who have suffered from austerity, and this alarmism is now spilling over,” he said. “The far right can only do well in periods of crisis, and the Brexit vote created a new and dangerous chapter of British history.”

Mr. Grover, who immigrated to Britain from Kenya and founded the Monitoring Group in 1981 after he was attacked by skinheads in the 1970s, said his group had received 15 calls on its emergency line over the weekend from immigrants who said they had been attacked verbally.

The Muslim Council of Britain said it had compiled a list of 100 reported hate crimes after the referendum result, including an attack on a teenage boy who was on his way to a mosque in East London on Sunday.

Nevertheless, the West Midlands police, which are responsible for law enforcement in Birmingham, a multicultural city with a large Muslim population, said that reports of 10 hate crimes a day over the past three days were in line with the daily average over the past three months, and the police in London reported no unusual increase in reported hate crimes.

Among those targeted in recent days were members of Britain’s large Polish community, which constitutes the largest number of foreign-born residents in Britain after Indians — 790,000 people, according to the latest data from the Office for National Statistics.

“London is a melting pot and you don’t expect this kind of thing,” said Joanna Mludzinska, chairwoman of the Polish Social & Cultural Association in Hammersmith, west London, whose building was vandalized with graffiti at the weekend. She was, however, gratified by the response, after being inundated with flowers and messages of support.

Scotland Yard is investigating the vandalism, but no arrests have been made.

In Huntingdon, a town in Cambridgeshire, north of the capital, the police said they were investigating reports from members of the Polish community that offensive leaflets were left on cars near a school as well as on several properties.