The financial means of people bringing environmental legal proceedings should not be the sole criterion when deciding whether the litigation is prohibitively expensive within the meaning of international law, the European Court of Justice (ECJ) ruled last week.
Campaigners have hailed the decision as helping to ensure that people can challenge decisions without facing huge costs.
Both EU law and the Aarhus Convention oblige member states and contracting parties respectively to ensure that environmental legal proceedings are "not prohibitively expensive".
Asked by the UK Supreme Court on how to interpret this either when assessing costs against an unsuccessful claimant or considering a costs cap, the ECJ said the national court "cannot act solely on the basis of that claimant's financial situation but must also carry out an objective analysis of the amount of the costs".
It continued: "It may also take into account the situation of the parties concerned, whether the claimant has a reasonable prospect of success, the importance of what is at stake for the claimant and for the protection of the environment, the complexity of the relevant law and procedure, the potentially frivolous nature of the claim at its various stages, and the existence of a national legal aid scheme or a costs protection regime.
"By contrast, the fact that a claimant has not been deterred, in practice, from asserting his claim is not of itself sufficient to establish that the proceedings are not prohibitively expensive for him."
The case - R (on the application of David Edwards and Lilian Pallikaropoulos) v (1) The Environment Agency (2) the First Secretary of State (3) the Secretary of State for the Environment, Food & Rural Affairs (Case C-260/11) - concerned an unsuccessful challenge to the decision of the Environment Agency to approve the operation of a cement works, including waste incineration, in Rugby.
The claimant's solicitor, Richard Buxton of the eponymous specialist Cambridge firm, said: "This is a tough steer from the European court that people must be able to take environmental claims without fear of having to being deterred by costs claims from wealthy opponents. The judgment emphasises the basic right for citizens to effective remedies and wide access to justice."
Mrs Pallikaropoulis added: "I hope this means I won't have to pay the exorbitant costs claimed by the government simply for standing up for the environment in Rugby."
Carol Day, solicitor at WWF and the coordinator of the Coalition for Access to Justice for the Environment (CAJE) said: "For far too long, legal action to protect the environment has been confined to either the very rich or the very poor, with the vast majority of concerned citizens powerless to challenge the decisions of public bodies. The judgment confirms that the government must ensure the public at large can exercise their democratic right to go to court."
Jake White, legal adviser at Friends of the Earth, another member of CAJE, added: "The judgment marks a significant step forward in the campaign to ensure that people are not prevented from obtaining justice in environmental cases purely on the grounds of cost. Whilst that campaign is not yet won, this judgment nonetheless sends a message to governments across the EU that costs may not prevent people gaining access to the courts in these cases."
The ability of people to bring environmental cases because of the costs has been a long-running issue. CAJE argued that recent improvements to the costs rules for environmental cases which came into force on 1 April do not go far enough. Cost caps that individuals and environmental groups would have to pay to public bodies if they lose judicial reviews are too high, it said, and a cross-cap - which limits the amount that successful claimants are able to recover - will make it very difficult for individuals and civil society groups to find lawyers to represent them in environmental cases.