Volunteers distributing food and water to homeless refugees and migrants in Calais are systematically being harassed and intimidated by French police, according to a report submitted to France’s human rights ombudsman.

Four associations working to distribute aid on the northern French coast, including the British group Help Refugees, published a report on Wednesday saying that between November 2017 and July 2018 there were more than 600 incidents of intimidation against volunteers.

These rangedfrom excessive identity checks and police stop and searches to arbitrary parking fines and pat-downs, threats, insults and verbal and physical violence.

The report said there had been 37 incidents of physical violence, including police pushing aid workers to the ground, snatching phones and forcing people away from areas where food was to be handed out.

In some cases British volunteers were being singled out by French police who were preventing them from giving out food and water, the report says. Volunteers with British passport or British vehicles were monitored and prevented from entering an area near Dunkirk on the French coast to distribute meals where refugees and migrants were sleeping rough. They were told “English associations” were not authorised to be there.

Volunteers with Refugee Community Kitchen preparing food for homeless migrants at Calais in 2016. Photograph: Antonio Olmos/The Observer

Maddy Allen, the Help Refugees field manager in France, said: “Violence and intimidation has been reported against volunteers of all nationalities, but British volunteers have been specifically targeted, particularly over aid distribution around Dunkirk. This is extremely concerning. It seems completely arbitrary and the authorities have no legal right to stop and target British volunteers.”

Allen said French police were tail-gating vehicles and staging stop and searches and pat-downs in the area. “Our human rights observer teams are on the ground in northern France to monitor police harassment of refugees and they noticed a spike in harassment of volunteers as well. The aggression we experience is a fraction of what is experienced by refugees in Calais and that is really worrying.”

Following the closure of a vast makeshift migrant camp in Calais in October 2016, hundreds of people are sleeping rough on France’s northern coast in squalid conditions and without proper access to sanitation.

Charities and NGOs trying to distribute food and water in Calais took court action last year, saying police and local authorities were preventing them from providing basic aid.

A refugee washing clothes on the ground at a Calais migrants’ camp, France, in August 2017. Photograph: Alicia Canter/The Guardian

Amid a large police presence in Calais, people are regularly moved on and their tents are taken. Last year Human Rights Watch said police were abusing migrants around Calais in the hope of moving them on, using pepper spray and confiscating belongings. In July a court ruled that the state had to build latrines for those sleeping rough.

The report by the aid associations, handed to the rights ombudsman of France, concludes: “French authorities are not just ignoring their human rights obligations but actively restricting humanitarian initiatives by volunteers in Calais.”

The volunteer groups said police were enforcing physical searches of aid workers, specifically targeting women.

Volunteers said police were preventing food from being distributed by issuing multiple parking tickets for vehicles, placing large boulders in the road to stop vehicles getting through and threatening volunteers with being taken to the police station for questioning.

The alleged violence included shoving, pushing and teargassing by the police. Verbal insults included officers telling two volunteers crossing a road: “It would be a shame if you got run over, arseholes.”

Éléonore Vigny, a legal expert at the French association L’Auberge des Migrants, which took part in the report, said that although it was a criminal offence to help non-documented migrants enter France or shelter them, it was not illegal to distribute food, clothing and water. “What we are doing is absolutely legal,” she said.

The Pas-de-Calais prefect’s office denied the allegations made in the report. In a tweet, the prefect’s office said police did not harass volunteers, and added: “Anyone who feels they have been witness or victim of a breach [by police] can go to the justice and administrative authorities.” It said: “No conviction or accusation relating to these allegations had been made.”