The decision is a small victory for the British Union for the Abolition of Vivisection (BUAV), who accused the government in court of failing to adhere to the 1986 Animals (Scientific Procedures) Act when granting experimental licenses.
The Act was implemented to keep animal experimentation at bay, as well as ensure that during any experiments that do take place, suffering is kept to a minimum.
The UK's Home Office currently does this by classing experiments as likely to cause 'severe', 'moderate' or 'mild' suffering before an experimental license is granted.
The case against the Home Office was based around a ten month undercover investigation carried out by the BUAV at Cambridge University's primate research facility between 2000 and 2001, relating to experiments on marmosets (monkeys).
The investigation revealed that at this facility, marmoset endured highly invasive brain surgery - sometimes with either no or very minimal painkillers.
In addition, it challenged the Home Office's label of 'moderate' suffering to experiments that contained highly invasive procedures, including inducing strokes by removing the top of marmosets' heads.
The BUAV argued that this is against the guidelines of the Animals Act, which states that any procedure that "may lead to a major departure from the animals' usual state of health and of well-being" must be categorised as 'substantial', therefore subjecting it to much more rigorous assessments before licensure is granted.
A judge agreed with the BUAV last week, ruling that the Home Office acted "unlawfully" in the licensing of brain experiments on marmosets at the University, based on their classification of them causing moderate rather than substantial "pain, suffering, distress or lasting harm."
The Home Office has now been ordered to undertake a review into its processes, although the ruling does not mean that any changes will actually have to be made, and it also has the right to appeal the decision.
The impact that any changes stemming from the review may have on the UK's animal research industry is unclear.
Commenting on the ruling, a spokesperson from Covance, Dr Chris Springall, told Outsourcing-Pharma.com that it was "a one-off finding...
I do not believe there will be any substantial changes as a result of this."
"All the work we do is subject to Home Office legislation and I have always found the inspectors very rigorous.
I have a lot of respect for them," said Springall.
"The key thing [about the ruling] is that there was no hint of a finding against the principle of using animals in research," he added.
Huntingdon Life Sciences were asked by Outsourcing-Pharma.com to comment, although failed to do so by the time of publishing.
Meanwhile, the judge rejected two other allegations made by BUAV that Cambridge's primate facility had inadequate staffing and monitoring arrangements in place; as well as the claim that animal death and suffering should be considered as part of cost-benefit assessments, to which the BUAV is not permitted an appeal.
Commenting on the ruling, a government spokesperson has said that it was "disappointed" at its failure to defend all aspects of the BUAV's claim, believing it "has been rigorous in applying the strict criteria of the Animals Act."
These comments come at a time when the number of animal experiments being conducted in the UK is on the rise, according to newly-released government figures.
Almost 3m animals were used in experiments in the UK in 2006 - a 4 per cent increase on 2005 and the highest number since 1991.
However, mice remain the mainstay of such experiments (69 per cent), followed by rats (13 per cent), while dogs, cats, horses and non-human primates account for less than 1 per cent.