At least 45,000 farmers have yet to fill in their agricultural waste exemption forms despite the deadline being just five weeks away.

Latest figures from the Environment Agency suggest that tens of thousands of farmers are sitting on their registration forms even though the deadline for their return – as with single farm payment applications – is 15 May.

Producers are required to apply for exemptions under the Agricultural Waste Regulations, which introduced a ban on the burning, tipping and burial of farm waste in spring 2006.

Farmers who apply for exemptions will still be able to carry out activities such as using tyres on a silage clamp or disposing of rotten potatoes on their land without having to get a full waste management licence.

Richard Bernhardt, waste policy adviser for the Environment Agency, said the agency had sent out 100,000 packs to farmers in England and Wales but so far only 30,000 had been returned.

“Numbers have been increasing since the start of the year, but there are obviously a large number of packs sitting out there under piles of paper that haven’t been returned,” he said.

“Our message to farmers is that the deadline is rapidly approaching so they should fill it in and send it back. It is a very simple process.”

Mr Bernhardt said farmers would still be able to apply for exemptions after 15 May but they would be more likely to get an inspection if they applied after the deadline.

Robert Caudwell, NFU waste issue spokesman, said the union thought about 75,000 businesses – not the 162,000 originally estimated by the government – would need to apply for exemptions.

“It is absolutely vital that people register their exemptions as soon as possible,” he said.

“Exemptions are free and a one off process – it only takes a couple of hours at most. It has been shown that if farmers want to maintain public support then we need to show we care for the environment.”

A spokeswoman for the Scottish Environment Protection Agency said it was not possible to say how many farmers in Scotland had still to register for exemptions.