Environmental campaigners have launched a High Court legal challenge against the temporary relaxation of a ban on pesticides which they claim are harmful to bees.

In July, an emergency 120-day approval was granted for the most at-risk oilseed rape growers in Suffolk, Cambridgeshire, Bedfordshire and Hertfordshire to use seeds treated with neonicotinoids – chemicals banned by the EU two years ago due to fears over their impact on bees.

But now the Friends of the Earth has confirmed it has applied to the High Court for a judicial review of the decision, which it claims did not comply with EU law which sets out the conditions under which governments can grant emergency use of restricted chemicals.

Friends of the Earth bees campaigner Dave Timms said: 'We believe that allowing farmers to use these 'banned' pesticides is unnecessary, harmful and unlawful.

'These neonicotinoid pesticides have been restricted throughout the EU because scientists say they are harming bees, which are crucial for pollinating Britain's fields, allotments and gardens.

'The government should be listening to the science and championing the long-term interests of our threatened bees.

'The distribution of these seeds should now be halted until the courts can decide whether their use is lawful.'

The environmental charity said a study, published last week, linking losses of honey bee colonies with the use of one of the banned neonicotinoids – called imidacloprid – added further weight to the evidence against this type of pesticide.

Neonicotinoids were previously used to protect crops from damage by cabbage stem flea beetles. Despite the removal of the chemical, agricultural consultancy ADAS estimates that the UK oilseed rape yield for 2015 will be 3-9pc higher than the national 10-year average – although farmers' leaders pointed out that the same report shows the lowest-yielding crops tended to be found in areas where factors such as beetle damage were a particular issue this season.

A Defra spokesman said: 'The government makes decisions on pesticides based on the recommendations of senior scientists and independent experts who have looked at the best available scientific evidence.

'It would not be appropriate for us to comment further on ongoing legal proceedings.'