Four former Conservative environment secretaries have warned the government against cutting a fund that pays farmers in England to plant woodland and improve water and soil quality alongside producing food.
The Environmental Land Management Scheme (Elms) was devised by then-minister Michael Gove following Brexit to replace the EU's common agricultural policy.
Earlier this month, the Guardian reported that Labour ministers were planning to cut the fund by £100m.
A Department of Food and Rural Affairs source told the BBC "no decision had been made" on the budget.
Writing to the Telegraph, the former ministers said the scheme had become "increasingly popular" and urged ministers to keep the farming budget "intact or - better still - increase it in line with inflation".
They added: "Farmers across England are now paid public money to deliver public goods... this can help them to become more resilient to nature loss, the biggest long-term threat to our food security."
The former ministers said the reported cut would "reduce the amount of farmland under the new schemes by 239,000 hectares in England at a time when food security and our natural environment have never been more important."
The letter was signed by Michael Gove, Andrea Leadsom, Therese Coffey and Theresa Villiers along with six other former Conservative farming and environment ministers.
It comes after a government report confirmed there had been a £358m underspend in the agricultural budget across last three years.
National Farmers' Union President Tom Bradshaw said news that the money had not been spent was a "kick in the teeth".
He said the underspend was not because "the investment isn’t needed" but a result of problems with the implementation of the scheme.
The previous Conservative government said the aim of the fund was to reward farmers for delivering "public goods" and making "a significant contribution to the environment".
The fund supports farmers and landowners to carry out projects such as large-scale tree planting and restoring coastal habitats.
In January 2022, the Public Accounts Committee criticised the scheme for failing to provide enough detail, meaning farmers had been unable to take advantage of the money available.
Kitty Thompson from the Conservative Environment Network said cutting the budget was "as short-sighted as it is foolish".
The letter from former Conservative ministers came on the same day that Conservative leader Rishi Sunak pressed the prime minister to make other commitments in relation to farming.
Speaking in Prime Minister's Question Time, he asked Keir Starmer to introduce a national food security target into law and to ensure good quality agricultural land would be used for food production rather than solar farms.
Starmer said he took food security "very seriously" but did not commit to introducing a legally-binding target.
The NFU has long-called for such a target to ensure enough food is produced in the UK.