The Environment Agency should be investigated for failing to seek out and punish farmers who were unlawfully causing nitrogen pollution but the watchdog was yet to act, two green groups have said.

WWF and ClientEarth said it had been over a year since they complained to the Office for Environmental Protection (OEP) that the Environment Agency had been “missing in action”.

The job of OEP is to hold government bodies to account and WWF and ClientEarth have questioned whether it is struggling to fulfil its duties.

OEP said the delay was due to “complex matters” that “have to be looked at thoroughly and in detail”.

The green groups said they had complained after a freedom of information request revealed that between January 2020 and December 2021, the Environment Agency conducted 2,213 inspections and found almost half the farms it visited to be in breach of agricultural regulations.

After the pandemic restrictions, in the year 2022/23, the number of inspections rose to 4,137, with 37% of those found to be in breach.

Despite the rise, WWF and ClientEarth said these inspections accounted for only 4% of the total number of farms in the country, meaning that many more instances of pollution were going unrecorded and unpunished.

Kate Norgrove, executive director of advocacy and campaigns at WWF, said: “At a time when the UK should be accelerating action on climate change, we are shocked that there has been no answer on if an investigation will take place, and fear that expectations have been raised by the Government’s watchdog that are not being met.

“To turn things around for England’s rivers we need those responsible for pollution to be held to account, and we need urgent action to support our farmers to protect river health.

“With the Environment Agency still missing in action, we urge the OEP to at last fulfil its mandate and act now to investigate this abject failure to protect our environment.”

Nitrogen is a vital element for plant growth and is used in synthetic fertilisers as well as being present in animal manure, which is also spread on fields.

But around 80% of this nitrogen is wasted as its inefficient use means plants do not absorb all of it and it is then washed into the soils or rivers.

Various chemical compounds of nitrogen affect the environment in different ways. In rivers, it can fuel large algal blooms that choke out other wildlife by consuming all the oxygen in a river.

Nitrous oxide, a gas, contributes to the greenhouse effect driving climate change and it is 300 times more potent than carbon dioxide.

Ammonia, another gas product of agriculture, is toxic to humans and a significant source of air pollution.

Helen Venn, OEP’s chief regulatory officer, said: “The OEP continues to look into the complaint received from WWF and ClientEarth and has engaged with all relevant public authorities about the issues raised, and some wider issues being considered as part of our work in this area.

“We have now received responses from all of the public authorities subject to the complaint. This includes a response from Defra which did not fully address the information requested and we are therefore continuing to discuss this with them.

“In the meantime, we are progressing our assessment of the matters where we have sufficient information to do so.

“We understand the concerns about the time this work is taking, but these are complex matters and have to be looked at thoroughly and in detail. We need to engage with the parties involved so that we have all the relevant information needed to make an informed decision.”

The Environment Agency has been contacted for comment.