Their comments come as the Pesticides Safety Directorate's (PSD's) updated agronomic assessment into the latest proposals confirms that while the overall number of chemicals under threat is now reduced, the implications of product losses for horticulture remain serious.
Prime minister Gordon Brown slammed the approach taken to formulating the new rules in a letter to the Crop Protection Association (CPA) last week, saying it "goes well beyond the risk-based approach to regulation that is advised by the UK's scientific establishment".
Trialogue discussions were still underway between the European Council, European Commission and European Parliament (EP) representatives to try to reach a compromise on the major issues as HW went to press. The latest meeting was due to take place on Wednesday (17 December).
A compromise has already been reached on "candidates for substitution" giving seven years to develop a replacement for a non-approved product. The European Council and European Commission wanted 10 years and the EP's environment committee five.
CPA chief executive Dominic Dyer said: "The goalposts keep changing so we are still not sure how many products will be lost. We are continuing to press the case for an impact assessment as there could still be serious damage done."
One of the major sticking points in the trialogues - set to have been hammered out during Wednesday's meeting - is the absence of a definition for "endocrine disruptors", one of a set of key criteria that could see a chemical banned.
It is proposed that a temporary definition be used, which could mean that a product is lost under the temporary definition, only to have its status changed when a full definition is in place, warned NFU plant health specialist Paul Chambers. "We will continue to support calls for an impact assessment but that might have to be done after the legislation is approved."
Robert Sturdy MEP, who sits on the EP's environment committee, presented a petition to Downing Street last week urging the Government to demand a Europe-wide impact assessment.
"If this legislation is put in place then in around two to three years' time a lot of the products grown in Europe will not be able to be grown," he said. "Just look at asparagus - it could be devastated by some of this legislation. I have an asparagus grower in my constituency and he's very worried."
Even with a positive result from the trialogue discussions, an impact assessment remained "absolutely crucial", he said.
Meanwhile, Rothamsted Research scientist Ian Denholm presented a separate petition signed by 72 scientists, which stressed their concerns about increased resistance to approved products.
Denholm hit out at the lack of clarity over criteria that will be used in the legislation.
He said: "Like a lot of people who have engaged in this debate we would like to see all the issues considered in a very comprehensive EU-wide impact assessment, particularly the issue of resistance."
He added that protected crops, as well as field brassicas, were of particular concern in this area.
The full plenary vote is expected to take place on 12 January in Strasbourg.
To read our comprehensive coverage on the EU pesticide proposals, click here.