The Conservators of Therfield Heath and Greens have been criticised for keeping the car park opposite McDonald's open, amid the rat infestation.

The conservators released an initial statement informing residents of the rat baiting in the area around the Therfield Road cark park on April 18, in response to an order by North Herts District Council under the Pest Control Act 1949.

The process to rid the heath of the infestation involves poison being placed by pest controllers into secure bait boxes, which are then placed within the litter bins' bases.

Speaking of authorising the use of the bromadiolone poison to cull colony of over 100 rats, the conservators said last week they were in a "difficult position, balancing the risks to humans and the heath’s wildlife and ecology".

Conservators chair Clare Swarbrick told the Crow last Friday: "Once NHDC contacted us under the Pest Control Act 1949 we had to act and during the risk assessment we looked at all the options and worked with a pest control expert."

There has been a mixed response to the conservators' actions, with the local wildlife group saying it was unfair they were bearing the brunt of the criticism when heath users not taking their rubbish home was where the infestation stemmed from.

There has been criticism of the use of poison - which can risk secondary poisoning to birds - including protected birds, who could ingest the rats - and other animals who may come across the poison or rodents.

The poison is legal, but the Barn Owl Trust warns against using bromadiolone to exterminate rats. On the trust's website it states the poison is a "very toxic second-generation anti-coagulant. Inhumane. Death is very slow. Bait covering ineffective. High risk of secondary poisoning. Widely available. Avoid where Barn Owls are present."

The RSPB said: "The key thing is that baiting is done professionally using bait stations that prevent other animals getting to it."

Questions have also been asked about why the car park is still open, given the "risk to public health".

Royston's Richard Ketteringham told the Crow: "If it is serious enough to use poison, the the car park should be closed.

"The conservators are not taking it seriously - what concerns me is it's a public health emergency and they are not acting like they've got a public health emergency.

"And laying down the poison is a bigger risk to wildlife and dogs. If the conservators and North Herts District Council want to show they are taking it seriously, close the car park and get rid of the waste."

Conservators chair Ms Swarbrick said: "The rat infestation is being taken seriously by the conservators. "All options were considered before taking action, including closing the car park to cut out food waste and litter.

"We discounted this idea initially due to the likely public safety issues this will cause when visitors cars are displaced on to Therfield Road, as well as the litter and uneaten food.

"Taking advice from a professional pest controller and working with Natural England, NHDC, the Health & Safety Executive and McDonald's, we were advised to adapt the existing bins to stop the rats getting in, and also put bait under the bins.

"We were strongly advised not to remove the bins in the first instance.

"Due to the seriousness of the problem, inspections are being made daily by at least one of the conservators as well as regular visits by our appointed pest controller. New rat resistant bins, sponsored by McDonald's are on order and will be installed as soon as possible.

"We may have to close the car park if the current measures don’t work. However, we hope to avoid this, and consider the measures taken to be the most appropriate at this time and will keep this under constant review after each of our daily visits."

Last week NHDC said: "It is the responsibility of each land owner to manage the infestation of pests on their land. If this is contracted out, the landowner is still responsible to ensure that any chemicals used are legally permissible and that the pest control processes followed are as safe as practicable, so as to ensure that the public and any non-target animal species are not endangered."

When the Crow told NHDC of concerns that the infestation was not being taken seriously, a spokeswoman said the authority had no further comment to add - reiterating "it is up to the owners of the land to decide on the most appropriate course of action to deal with the infestation, and DEFRA are responsible for policy on pesticides, for approval and enforcement."