A third farm has been closed following fears of an E.coli outbreak, the Health Protection Agency (HPA) said today.
White Post Farm in Nottinghamshire has shut after it was confirmed that a second person was suffering from the same strain of E.coli as a previous visitor.
Godstone Farm in Surrey closed last Saturday and its sister farm, Horton Park Children's Farm in Epsom, is also shut because of "unsatisfactory" hygiene arrangements.
A statement from the HPA said: "The farm has closed voluntarily and the HPA and its partners are conducting a full epidemiological investigation.
"The Agency is also aware of two other cases potentially linked to the farm who have had different strains of E.coli O157.
"There are many potential sources of E.coli and as yet there is no confirmation that the farm is the source of infection in these cases, all of whom are well.
"The majority of E.coli outbreaks are caused either by food contamination or person-to-person spread and only about one in 50 of all cases are associated with outbreaks linked to petting farms.
"Where there are different strains of E.coli involved, as there are in this case, there is uncertainty about whether there is a shared source of infection.
"The HPA has advised closure of the farm on a precautionary basis to protect the public health while the investigation continues."
There are currently 45 cases of E.coli linked to Godstone Farm in Surrey.
Of the 45 affected, 12 are children being treated in hospital. Four of them remain seriously ill.
Six children are in a stable condition, and two were described as "improving" by the HPA yesterday.
An HPA spokeswoman said it was not aware of any cases of E.coli O157 linked to Horton Park Children's Farm.
"The hygiene arrangements were found to be unsatisfactory and the HPA advised the local authority that the farm should be closed immediately while these defects were rectified."
A spokeswoman for Horton Park Children's Farm said the decision to close the farm was made because of the perceived "slight risk" of more children contracting E.coli.
A statement said: "Horton Park Children's Farm has decided that, owing to concerns expressed by us and others, and due to the slight risk to our customers of the chance of the disease, the farm will close as a temporary measure until we and others are satisfied that everything in our power has been done to eliminate or reduce any potential risk to our customers and friends.
"I must impress that Horton Park Farm has no suspected or actual cases of E.coli and that this is a preventative measure taken by us to safeguard all our friends and customers."
The parents of the most ill children have been given an apology by the HPA for delays in closing Godstone Farm and an independent investigation has been commissioned.
Tracy Mock, the mother of two-year-old twin boys Todd and Aaron Furnell, said she was "encouraged" by the progress they were making at St Thomas' Hospital in central London.
Anthony Moore, spokesman for White Post Farm, said: "We closed voluntarily this morning and would like to stress that it is purely a voluntary and precautionary matter.
"We have been advised that the outbreak is potentially and tenuously linked to us and, given what has happened in Surrey, we took the decision to close voluntarily.
"The HPA thought it important to do some tests and we thought it important to close while they do so.
"There is no confirmation that the infection has come from here.
"We should know the results of the tests by Monday."
The HPA said the total number of E.coli cases linked to Godstone Farm in Surrey now stands at 49.
Nine children remain in hospital, with one due to be discharged today.
The rest of the children remain stable.