The Government is "worryingly complacent" about the challenge of ensuring environmental standards are maintained following Britain's exit from the EU, a parliamentary report has warned.
Ministers face an "immensely complex task" in creating a post-Brexit regime which disentangles the UK from the web of EU regulations and standards while ensuring Britain's environment remains as well-protected as it has been, said the House of Lords EU Energy and Environment Sub-Committee.
Under the terms of any trade deal with the remaining 27 EU states, Britain may still be required to comply with continent-wide environmental standards, while losing any influence on shaping them, the report warned.
The Department for the Environment, Food and Rural Affairs will need a "substantial increase in resources" to maintain environmental legislation while developing domestic agricultural and fisheries policies, it said.
And it warned that if the UK fulfils Prime Minister Theresa May's aim of withdrawing from the jurisdiction of the European Court of Justice, a new domestic mechanism, underpinned by judicial oversight, will be needed to fill a "vacuum" in the enforcement of standards.
The committee warned that domestic environment legislation and policy will be "more vulnerable to short-term, unpredictable changes" after Brexit, threatening investor confidence in the sector.
It called on ministers to make clear whether funding for environmental research and green infrastructure development currently received from the EU and European Investment Bank will be maintained after Brexit.
And it urged them to identify other countries and groups with which the UK could ally itself post-Brexit with the aim of maintaining its role as a "global leader on climate action" and mitigate any loss of influence caused by EU withdrawal.
The report cited polling suggesting that 80% of the public want environmental protections to remain as strong after Brexit.
But committee chairman Lord Teverson said the cross-party panel was "not convinced that the Government has yet found a way to deliver the continuity of environmental protection that we all want to achieve".
Lord Teverson said: "The European Commission and the Court of Justice have played absolutely vital roles in monitoring and enforcing environmental law in the UK.
"The bottom line is that if the UK fails to honour EU environmental law, it will end up in court. That's going to change after Brexit, but the vast majority of our witnesses were emphatic that an effective and independent domestic enforcement mechanism will still be needed.
"Co-ordinated global action is required to tackle climate change. The UK has been a world leader, but in leaving the EU we lose our strongest allies, and we'll need to identify other countries to align ourselves with, to make sure we continue to lead and influence global climate action."
A Defra spokesman said: "Our ambition is to be the first generation to leave the environment in a better state than we found it.
"We are committed to building on our long history of wildlife and environmental protection and securing the best deal for Britain as we leave the EU.
"We are clear that we are ready to deliver all of this Government's priorities and will continue to build the right skills, experience and leadership to deal with the challenges, and take advantage of the opportunities, that lie ahead."