The HTA has reiterated there is no evidence of danger to gardeners from using glyphosate-based products bought in garden centres in the wake of calls from a pressure group to stop selling them.
The Pesticides Action Network (PAN) has written to B&Q, Homebase, Dobbies, Notcutts, Wilko, Wickes and all main supermarkets to ask their position on the sale of glyphosate products.
Several retailers have re-examined their policies on stocking glyphosate products following its classification as "probably carcinogenic" by the World Health Organisation's cancer agency.
A Dobbies representative said: "We are looking into the new information on glyphosate and the different decisions being made across Europe before making a decision on how this may or may not affect our policy."
HTA horticulture head Raoul Curtis-Machin said: "There is no evidence of any danger to gardeners from using glyphosate bought from a garden centre and used according to the label instructions. Rigorous testing is carried out on garden retail chemicals to ensure their public safety as a condition of their sale.
"The reality is that there is no evidence or advice of risk. Glyphosate has been used for more than 40 years, based on rigorous testing, and there continues to be a huge number of tests carried out to ensure public safety."
PAN policy officer Nick Mole said the move followed West Six and North One becoming the first UK centres to stop selling Roundup, the removal of glyphosate products from German and Swiss retailers, the International Agency for Research on Cancer (IARC) classifying the herbicide as "probably carcinogenic" and French political moves for a ban.
"We are not going to attack retailers just yet, if at all," said Mole. "We'll try and keep positive because it's not just about human health, it's also about water pollution." He said he wants to "motivate the public" and said legislation around the Water Framework Directive and sustainable drainage systems means the issue is of wider amenity concern.
Areas such as Brighton, Witney, Falmouth and Hackney are being pressurised to ban public use of the chemical. Mole wrote: "Not only is glyphosate a probable carcinogen it has also been linked to birth defects and other health problems."
Monsanto business director Gary Philpotts said the network "whips up fear and activity among a few people" and is "irresponsible" when talking about areas such as cancer in children where there is "no credible evidence" that glyphosate is responsible. He added: "It's true some retailers have decided not to stock because of the pressure." But he said consumers just go and buy from another store.
"Everyone is concerned about the pressure but more retailers will understand than give in," said Philpotts. "Retailers shouldn't be fearful." The German Federal Institute for Risk Assessment - the EU member state "rapporteur" for the glyphosate renewal process - said glyphosate is unlikely to pose a carcinogenic risk, he added.
"My message to UK retailers is it is safe to use in your garden and approved across Europe and pretty much the whole world." Products such as Weedol, Roundup and Resolva provide a "safe and effective solution on the shelf" and the issue is about "responsible use", he said.
Crop Protection Association chief executive officer Nick von Westenholz said: "It is disappointing to see pressure groups misrepresenting the science in using this classification to promote their own agenda, whipping up concern despite glyphosate's excellent safety profile."
BALI technical director and Ground Control national training manager Neil Huck said if Hackney becomes a glyphosate-free zone the council will have to bear the extra cost. Ultimately contractors will work to client specifications, but residents must recognise that it will be more expensive, he added.
Defra's five-year Thanet Weed Project, which studied various weed-control options, found an integrated management approach combining less-frequent glyphosate applications with non-chemical control is, over time, as effective as more regular glyphosate use, but costs around twice as much.
Huck said: "It depends if the residents want to pay several times more for an alternative method or if they don't want to have weed control in the borough at all." Although the IARC report has raised concerns among Ground Control clients they are generally reassured when the contractor explains that the bulk of the research shows glyphosate is safe, he added.
Amenity Forum chairman John Moverley insisted that any decision by a local authority to ban glyphosate "should be based on the science and the evidence - and the current situation is that it is a very safe product". Recent publicity around invasive species such as hogweed has highlighted the importance of weed control in amenity areas, he said.
German retail group Rewe has banned the sale of products containing glyphosate from its 350 DIY stores. Swiss companies Coop and Migros have also stopped selling glyphosate products. Glyphosate, a herbicide, is the active ingredient in 223 products that are available in the UK, including well-known product Roundup.