A record number of councils in England and Wales are using private companies to issue fines for littering and fly-tipping amid concern that some contractors are adopting unscrupulous tactics to profit from people.

Littering penalties are set to rise as part of a crackdown on antisocial behaviour. The environment minister, Rebecca Pow, said the maximum amount people caught fly-tipping could be fined would more than double from £400 to £1,000. Those who breach their household waste duty of care could be fined £600, up from £400.

In 2021-22, English and Welsh councils dealt with almost 1.1m fly-tipping incidents and issued 91,000 fines, along with other enforcement actions. In early 2022, freedom of information data from the civil liberties campaign group Manifesto Club showed 66 councils employed a private company to issue fines for environmental offences such as fly-tipping, dog fouling and smoking in prohibited areas. This year 76 councils are employing private firms, up 10 in a year.

But critics have expressed concern about how some of these companies are operating. People who spoke to the Guardian complained of being fined for feeding birds, for putting their bins out at the wrong time, and being falsely accused of fly-tipping. They have accused companies of not having clear appeals policies and of threatening people with court, wrongly stating it is up to them to prove innocence. In UK law it is up to the prosecuting body to prove guilt.

One company, 3GS, was awarded a £2.9m contract for enforcement services in Waltham Forest in April 2021. In its first nine months on the job, the Waltham Forest Echo found they issued more than 7,500 fines – of which 5,000 were for littering cigarette butts.

Last year, 3GS lost a contract with Manchester city council. The council said the contract ended and after a tendering exercise a new one was appointed. 3GS took about 75% of all profits made from litter fines, the council said.

They added: “A percentage of the receipts from paid FPNs (fixed-penalty notices) was retained by 3GS but from this, the company was expected to cover their costs in running the service – ie staffing, equipment and other overheads.” Manchester council said it never set targets on the number of FPNs.

In September 2019, the Department for Environment, Food and Rural Affairs produced guidance seeking to rein in the practice of issuing fines for profit. This guidance said enforcement should not be used as a means of raising revenue. However, this guidance is non-statutory and therefore in practice it is ignored. Defra is looking at making the guidance statutory.

Josie Appleton, the director of the Manifesto Club, said: “The corrupting practice of paying companies per fine should be outlawed. It does nothing for cleaner streets, and just means that members of the public are hassled and unfairly targeted. Enforcement should be carried out by public officers enforcing the law fairly and in the public interest. Defra plans to restrict ‘fining for profit’ with upcoming statutory guidance, but it’s essential that this guidance has teeth so that it actually changes practice on the ground.”

One former worker at 3GS, who joined in 2019, alleges officers working for the company were expected to upload figures for how many fines they had issued at the end of the day. He claimed people were criticised for not hitting targets of five fines a day, and threatened with being dismissed. “If you uploaded figures and they were off-target you would be told you need to buck your ideas up,” they alleged.

They claimed: “It was purely financial … if you don’t hit your target a few days in one week then you don’t know what will happen.”

Under UK law, it is illegal to drop litter and people can be issued with an FPN by way of an on-the-spot fine or a letter sent to the person’s home address. Under the Environmental Protection Act 1990 people must give their personal details to a litter enforcement officer.

While there is no legal right of appeal to an FPN, it can be queried in the form of a “representation” in writing to the council. If an FPN for littering is disputed, the case will be resolved in court. Anyone found guilty may face a fine of up to £2,500.

In Waltham Forest, people have complained of being fined for fly-tipping after putting their waste outside at the wrong time of day. Carla Grande, a filmmaker, and her partner, John Rowe, say Waltham Forest council and its enforcement contractor sent them “round and round in circles” when they asked for their fine to be reviewed.

The couple put their bin bags out on the street below their flat at the wrong time soon after they moved in. Grande said it was hard to appeal against the fine but after numerous emails it was reduced from £400 to £250, the amount issued for littering offences. This was because the bin bags were “intended to be collected” rather than deliberately fly-tipped.

Speaking at a council climate change scrutiny committee on 27 March, Grande said: “I would like justification as to why this is, I believe that it’s because I am not going to give up.

“If it’s a littering fine, it should be a littering fine from the start, not a fly-tipping fine for putting bags out, not after sending emails for two-and-a-half months thinking I’m going to court.”

Nick Leader, who lives in Hackney, was accused of littering when a package with his address on it ended up in Waltham Forest. He had no idea how it got there. After disputing the fine with 3GS and the council, he consulted a lawyer. The council said it was Leader’s responsibility to provide evidence he did not drop the litter, but the legal adviser said this was not true.

The lawyer said: “I am surprised that the council has thought it fit to threaten the accused with a five-year jail term and an unlimited fine in this case given it has essentially no evidential basis (beyond its misconceived notion that there is a reverse burden on the accused to prove his innocence).”

Leader said: “They came with threats from the very beginning and what they were saying was not true but they would not budge, so I thought – should I just pay [the fine]? … It took a lot of time and hassle, legal advice … it was only when we escalated it to Waltham Forest council’s chief executive that they climbed down.”

Clyde Loakes, Waltham Forest council’s deputy leader and cabinet member for climate and air quality, said: “Waltham Forest spends upwards of £7m every year clearing up litter and fly-tips to keep local neighbourhoods clean and tidy as residents rightfully expect, and public bins are provided across the borough.

“Residents also have a duty of care to dispose of household waste correctly, and the onus is on them to show that they have taken reasonable care to do so. Our contract with 3GS does not contain any quotas for fines issued by operatives.”

3GS did not respond to requests for comment.