It's hard to imagine now, but it's not that long ago that David Cameron was still bandying about the slogan: "vote blue, go green." He once championed himself as a Tory moderniser on the environment. But we've come a long way since the days of trips to the Arctic and hugging huskies. Cameron now openly talks about "getting rid of green crap," while Tory minister Michael Fallon has said the Tories would stop the construction of onshore wind farms if they win in 2015. As we near the general election, the Conservatives are rapidly abandoning any pretence that they care about the green agenda.

Nowhere is this clearer than in the European Parliament, where the Tories are completely unrestricted by the constraints of coalition government. Time and again Conservative MEPs have shown their true colours when it comes to EU environmental measures, and they are definitely not green. They voted down EU measures to restrict the destructive practice of deep-sea fishing. They've opposed efforts to reduce plastic bag use and tackle the scourge of plastic waste in our oceans. And they've repeatedly voted against efforts to strengthen the EU's carbon emissions trading scheme, Europe's landmark policy for fighting climate change.

Yesterday, the Tories showed their true colours yet again when MEPs voted on EU proposals to tackle air pollution, which the new European Commission is threatening to withdraw or water down in its drive to cut red tape. This is being rightly opposed by many MEPs, including Liberal Democrat MEP Catherine Bearder who's leading the charge to keep these proposals on the table. We all want to see moves to make EU regulation smarter and more efficient, but that shouldn't come at the expense of the air we breathe. Air pollution now causes an estimated 29,000 premature deaths in the UK each year, almost as many as smoking. And with 40% of the most deadly pollutants coming from elsewhere in the EU, it's clear that we need urgent action on this across Europe.

Yet Conservative MEPs refused to stand up for these vital measures to improve air quality, voting against key amendments to prevent them being delayed and calling for them to be watered down to "reduce administrative burdens." It seems that for the Tories, laws that protect the environment and improve people's quality of life are just more red tape to be slashed. They fail to see that moving towards a cleaner, greener economy isn't just the right thing to do for the planet. It's the best to way to secure future growth and jobs.

The Conservatives' approach to the environment in Europe shows what sort of approach they would take if they are allowed to govern alone. In coalition, Liberal Democrats have fought to make sure that the environment has stayed at the top of the agenda. We've doubled the amount of energy generated from offshore wind and stopped the Tories from slashing support for renewable energy. And while senior Conservative politicians voice their doubts about man-made climate change, Energy Secretary Ed Davey has been busy paving the way for a global deal to cut carbon emissions. Without the Lib Dems, there would be nothing to stop the Tories from lurching to the right on the environment. The truth is, the only way to make blue go green is by adding yellow.

Tim Farron is Lib Dem MP for Westmorland and Lonsdale