The European Commission has delayed a decision on whether to enforce a blanket ban on controversial pesticides which have been found to be polluting East Anglian rivers.

Neonicotinoids are already banned in the EU for flowering crops like oilseed rape, after concerns were raised about their potential impact on the health of bees and pollinators.

But there are also concerns from environmental groups that the seed treatment chemical could find its way into soils and watercourses, posing risks to aquatic wildlife.

Earlier this week, the Wensum and Waveney were two of eight rivers across England that were found to be contaminated with neonicotinoid pesticides in tests conducted by the Environment Agency last year.

The Waveney was found to be acutely polluted while the Wensum, a Special Area of Conservation for its river life, was found to be chronically polluted.

The results were released by conservation charity Buglife in the same week that a decision was expected on the European Commission's proposals to extend current neonicotinoid restrictions to all outdoor crops – a vote which has now been delayed until 2018.

Chief executive Matt Shardlow said: 'It is vital that action is taken to completely ban these three toxins, including in greenhouses and on pets, before another year of disgraceful pollution occurs.'

Currently, the restrictions cover flowering crops, spring-sown cereals and maize. In the UK, the proposed extension of the restrictions would include all use on cereals, sugar beet and vegetable crops. Buglife said sugar beet fields were the most likely source of pollution in the Norfolk rivers.

But National Farmers' Union vice president Guy Smith, who will chair the Norfolk Farming Conference in February, said there was not enough scientific evidence to justify a complete ban.

'We believe the Commission should not make a decision until the European Food Safety Authority (EFSA) has published its review of the evidence on neonicotinoids next February and until the EU General Court has delivered its ruling on the legality of the initial restrictions,' he said.

'The NFU and its members will continue to make the case to politicians and decision-makers in both Westminster and Brussels that the evidence does not justify further restrictions and to highlight the impact a ban will have on farm businesses and food production.

'The NFU believes any decision should also take into account an assessment of the impact of restrictions on crop production.

'Farmers are acutely aware that bees play a crucial role in food production. Farmers rely on bees to pollinate crops and have planted around 10,000 football pitches of flower habitat across the country to support a healthy bee population and give them a good home – all because they recognise the key role they play in producing safe, affordable food.'