More work needs to be done to establish the environmental impact of drilling for natural gas under the Wadden Sea near Ternaard in Friesland, according to a government commission.

The commission has told economic affairs minister Stef Blok that the environmental report carried out into likely impact of gas extraction misses ‘essential information’ in some key areas, local broadcaster Omroep Friesland reported.

Blok said in September there is little that can be done to stop gas company NAM extracting natural gas from under the Wadden Sea because the decision to grant the permit was an administrative rather than a political decision.

The news that NAM, a joint venture between Shell and ExxonMobil, plans to extract up to 7.5 billion cubic metres of gas off the coast at Ternaard in Friesland has been slammed by green groups and some MPs. The Wadden Sea is a Unesco protected heritage site, and the UN body has also expressed its concerns.

However, Blok says the licence cannot be refused because the necessary research into the impact of drilling has been done. This research, he said, shows that there will be no damage to the natural environment although the sea bed may drop by a ‘limited amount’.

However, according the Commissie voor de Milieueffectrapportage, the original research does not sufficiently examine the impact on the salt marshes, breeding birds and what the drop in the sea bed will mean.

Nor does it look at the potential increase in nitrogen-based pollution or the damage to archaeological remains such as shipwrecks.

Environmental groups,  Friesland provincial council and the Noordoost-Friesland local authority have all made formal protests about the gas extraction plans.