The UK's membership of the European Union has been a "crucial factor" in driving polices on air and water pollution and protecting wildlife, MPs have said.
An inquiry by the parliamentary Environmental Audit Committee (EAC) found the "overwhelming view" of witnesses across the sector was that EU membership has been positive for the UK environment.
The committee's chairwoman, Labour's Mary Creagh, said: "The UK has cleaned up its act since we were dubbed the 'dirty man of Europe' in the 70s.
"EU environmental laws have played a key part, and mean we bathe on cleaner beaches, drive more fuel-efficient cars and can hold Government to account on air pollution."
EU environmental policy has led to improvements in standards on air pollution, water quality and protecting nature, a report by the committee found, with implications from witnesses that the UK government would set less stringent rules if acting alone.
But membership of the bloc has also given the UK a platform to pursue its environmental objectives, for example driving international efforts to tackle climate change as part of the EU - and being seen as a leader on the issue.
And in what was described as a "two-way street", the UK has also been a major player in the EU, ensuring action on the environment was taken on a faster timetable and more thoroughly than otherwise would have been the case, the report said.
On concerns that EU policy can be difficult to change once put in place, the report suggested this led to benefits such as allowing longer-term planning and greater certainty for businesses looking to make green investment decisions.
Ms Creagh warned that environmental problems did not respect national borders.
"When it comes to protecting our natural environment and dealing with global problems like climate change, the overwhelming evidence is that EU membership has improved the UK's approach to the environment and ensured that the UK's environment has been better protected."
But one member of the committee, Tory MP Peter Lilley, wrote a dissenting report, accusing the environmental groups who gave evidence of having vested interests because they received EU funding.
Either the EU has made Britain adopt higher environmental standards than it would have done otherwise, or the UK has pushed Europe to be greener - but both could not be true, he argued.
He also said environmental issues could be handled by co-operation between the UK and EU in the event of Brexit.
Peter Morris of the Wildfowl & Wetlands Trust (WWT) said: "We share our air, water and migratory wildlife with other countries.
"It makes sense to have a say in how our shared environment is protected. Our lives, homes and businesses depend upon it."
Sam Lowe, Friends of the Earth campaigner, said: "From climate change, to air pollution, to destruction of the natural world, this generation faces huge challenges which we cannot deal with alone.
"This report adds further evidence to the argument that Friends of the Earth has been making for months: the UK's environment is best served working together with our European partners."
Greenpeace UK chief scientist Doug Parr said: "We all know the EU isn't perfect, but it's a widely recognised fact that without its regulations our environment would be worse off.
"Whether you care about wildlife protection or poisonous chemicals in our food or holding the Government to account on air pollution, the standards set in Brussels have played a crucial role.
"If Britain leaves, we may have to fight all over again for environmental protections that we now take for granted."
A spokeswoman for the Government said: "This report clearly demonstrates the overwhelming environmental benefits of our EU membership.
"From banning fish being thrown back dead into the sea, to tackling climate change, the UK has led the way in driving up standards across Europe.
"By working together across the EU, we can protect and enhance the environment far more effectively, preserving our precious wildlife and natural resources for generations to come."
Pro-Brexit minister George Eustice said: "Our natural environment is rich in diversity but is also complex. Imposing centralised policies through clunky EU directives has failed because these act as a strait jacket that stifles innovation in environmental management.
"The UK has also lost its voice and voting rights on many international wildlife conventions.
"If we Vote Leave and take control, we will regain our seat at the table at these conventions. We would be able to innovate, to pilot ideas and to really deliver for our natural environment."