A protest group has been ordered to pay the legal costs of its WA Supreme Court action against the federal and state-funded Roe 8 highway extension in Perth's south.

Save Beeliar Wetlands last year successfully appealed the Environmental Protection Authority approval for the road, which is part of the $1.9 billion Perth Freight Link, with Chief Justice Wayne Martin saying the EPA “took no account of its own published policies” when it gave the green light and had been…