British agriculture will be devastated if Brussels presses ahead with plans to tighten pesticide restrictions, government scientists have warned.

Cereal yields will slump by up to one third and food quality will plummet under proposed EU legislation to reform the way pesticides are approved, reveals an in-depth study by the government's Pesticides Safety Directorate.

"Non-approval of the triazole compounds would remove the foundation stone of control programmes for the major disease of wheat in the UK, Septoria tritici, with potential for 20-30% yield losses," says the study.

Scientists assessed nearly 300 substances, including most conventional chemicals. The report concedes that some of the withdrawal impacts are difficult to forecast, but warns that they will still be severe.

"Blackgrass is the major grass weed species in England, and effective blackgrass control strategies rely on pre- and post-weed emergence sequences of a limited range of key herbicides," says the PSD.

"The non-approval of the pendimethalin pre-emergence option would jeopardise weed control, leading to yield losses, and would place increased risk of resistance on remaining active substances."

In total, EU Commission proposals could remove up to 15% of the substances assessed, some of which are particularly important in the UK to protect minor crops such as carrots and parsnips.

Further amendments by the European Parliament could result in the loss of up to 85% of conventional chemical substances available to farmers, according to the document, which was published on 9 May.

"If the full potential impact of the current [European] parliament proposals were realised, conventional commercial agriculture in the UK as it is currently practised would not be achievable, with major impacts on crop yield and food quality."

The PSD study echoes warnings issued last month by a group of leading scientists from seven European countries who said the proposals would increase disease resistance, making the cultivation of many crops problematic or uncompetitive.

European agricultural ministers will debate the proposed legislation this month.