Green campaigners have urged the European commission to ensure a post-Brexit trade deal guarantees a powerful environmental watchdog in the UK.

In his first official meeting since EU leaders signed off the Brexit deal, the EU’s chief negotiator, Michel Barnier, met eight of Europe’s biggest environmental groups on Monday, including Greenpeace, WWF and the Climate Action Network Europe.

Green groups have welcomed the 585-page withdrawal agreement and political declaration because they link the UK’s trading relationship with Europe to matching EU environmental standards. Along with social protections, state aid and competition laws, the environment is part of the “level playing field” that any British government must respect if it wants a close economic relationship with the EU.

Campaigners are now calling on Brussels to ensure that the UK’s environment secretary, Michael Gove, creates a strong watchdog as part of negotiations on the future trade relationship.

The groups want an equivalent to the European commission, an independent body that could take the government to court and issue fines for breaking laws on air and water quality, nature protection and waste management.

“The commission should be extremely vigilant and use the next couple of years to really verify that the UK is putting the right machinery in place,” said Ariel Brunner, the senior head of policy at Birdlife Europe, which was part of the delegation that met Barnier.

“This governance needs to be in place at the end of the transition period, either when the backstop kicks in or when the new relationship kicks in.”

The demands underscore the trade-offs the UK will face as part of the post-Brexit trade deal, which must be approved unanimously by 27 member states and their national parliaments. Preserving a level playing field, including on the environment, is a big priority for states closest to the UK, such as France, the Netherlands and Ireland, which would face the starkest competitive threat.

Gove has acknowledged that Brexit creates “a governance gap” to protect “voiceless” nature, but his plans have been heavily criticised by green campaigners, who see a “toothless body that is seriously lacking in legal punch”.

Alarm bells are ringing even louder after the outgoing chairman of Natural England, Andrew Sells, told a committee of MPs last week that the agency had “lost a great deal of independence” to the Department for Environment, Food and Rural Affairs.

The UK is more likely to be taken to court over environmental law than any other EU policy, according to the Institute for Government thinktank. The European court of justice has ruled against the UK government, in whole or in part, 30 times out of 34 cases brought by the commission.

Campaigners fear an erosion of nature protection standards would damage 76 habitats and more than 100 species of Europe-wide interest, such as Caledonian forest, the marsh fritillary butterfly, the puffin and the tufted duck. “The whole EU conservation system has been built with the UK in mind,” Brunner said. Brexit risks “punching a huge hole in the middle of the biogeographical region”, he added.