In February 2010, David Cameron made a speech at the University of East London in which he set out his vision for "rebuilding trust in politics". At the time, the Conservative party leader was just a few months away from the general election and the MPs expenses scandal was still very fresh in the public's mind. He used his speech to warn of a new scandal brewing:

I believe that secret corporate lobbying, like the expenses scandal, goes to the heart of why people are so fed up with politics. It arouses people's worst fears and suspicions about how our political system works, with money buying power, power fishing for money and a cosy club at the top making decisions in their own interest.

We can't go on like this. I believe it's time we shone the light of transparency on lobbying in our country and forced our politics to come clean about who is buying power and influence.

Last week, we got to see why Cameron was right to highlight the need for total transparency over lobbying. As the Guardian reported, Chris Huhne, the energy and climate change secretary, ordered a private inquiry into whether fossil fuel lobbyists had "got to" the Conservative MEPs who had recently voted against improving the European carbon emissions target. Analysis of the Tory MEPs' published lobbying contact register for 2010 revealed that, on average, they had had four times as many meetings with lobbyists from fossil fuel companies as with lobbyists pushing for deeper cuts in emissions.

Martin Callanan, leader of the Conservatives in Europe and an environment spokesman, responded: "Our position on [deeper emission cuts] has not been influenced by lobbyists and has remained unchanged since the idea was first mooted."

That we even know about these meetings with lobbyists is only possible because the Tory MEPs have volunteered this information themselves. For that - in stark contrast to politicians in rival parties - they should be congratulated. But, despite this welcome display of transparency, there is no getting round the fact that the register makes for unsettling reading.

Take Martin Callanan, for example. Callanan, who represents the north-east England constituency, was instrumental last year in steering weakened carbon emission targets for new vans through the European parliament. He won a fight which led to the proposed target of 135g CO2/km by 2020 being raised to 147g CO2/km. The talk at the time in Brussels was of "extensive lobbying" by the auto industry which was desperate to see the legislation weakened.

Thanks to the Tory MEPs' register of lobby contacts, we can now see exactly how often Callanan met with representatives of the auto industry – and other interested parties, such as delivery companies and environmental groups - throughout 2010 to discuss the van emissions legislation:

Ford x 5
Toyota x 4
Volkswagen x 4
Fiat x 3
European Automobile Manufacturers' Association x 3
Renault / Peugeot-Citroen x 2
Society of Motor Manufacturers and Traders x 2
Jaguar Land Rover x 2
General Motors
Federation Internationale de l'Automobile
German Association of Automotive Industry
Japanese Automobile Manufacturers Association
Albemarle
American Chamber of Commerce
Commercial Motor magazine
European Chemical Industry Council
European Newspaper Publishers Association
European Petroleum Industry Association
Federation of Small Businesses
Greenpeace / Transport and Environment (joint meeting)
NHS Europe
Novozymes (sustainable transport and biofuels)
Systems Capital Management
Liam Benham (trade unionist)
Transport and Environment
United Parcel Service / Deutsche Post DHL

Tot up all the times Callanan met with lobbyists representing either a vehicle manufacturer, or one of their trade associations, and you come to a grand total of 29 "contacts" across that 12-month period. By comparison, Callanan - the Tory MEPs' "environment spokesman", remember - met with environmental groups on just two occasions.

Readers can draw their own conclusions about whether this clear imbalance was either constructive or healthy, but one person who is unsettled by this revelation is Dudley Curtis, communications manager of Transport and Environment, the group which "campaigns on sustainable transport at the EU level in Brussels":

I once heard a top Brussels PR expert say that effective lobbying was telling the person you're trying to influence the same thing five times, in five different ways. Well, the motor industry met the guy in charge 29 times just to make sure he got the message. Those that might have an alternative take on the issue - the drivers association, the small business association, the environmental NGOs - were vastly outnumbered. One or maybe two meetings each compared to the massed ranks of the motor lobby. So the debate is bound to get skewed away from environmental arguments, let alone 'John the plumber' who might like lower fuel bills for his van.

More widely, it has been interesting to see the reaction of the Tory MEPs to close scrutiny of their register of contacts with lobbyists. We seem to have hit a nerve. Roger Helmer, a prominent climate sceptic, used his blog to rail against Huhne's "absurd and insulting" request for an investigation. Meanwhile, his colleague Julie Girling wrote to the Guardian, telling us not to "get too carried away". And Dan
Hannan - who refuses to meet with lobbyists as a matter of principle - claims that the "most intense lobbying in advance of the [emissions target vote last month] came not from Big Energy, but from Greenpeace, Christian Aid and the WWF".

Over at Conservative Home, Taxpayers' Alliance chief Matthew Sinclair, claims the influence of lobbyists is "a longstanding environmentalist myth".

All the MEPs we contacted suggested that the lobbyists had no influence on them. You can reach your own judgement on that. But there's more. Girling told us: "Personally, I try to meet with most people who request a meeting. I cannot guarantee a balance of requests between businesses and NGOs." Helmer made much the same point.

The problem, of course, is that this approach - open door to all - means those with the most money for lobbying get the most air time. And it certainly does not alter the fact that Conservative MEPs clearly see lots of fossil fuel lobby groups and are directly defying their prime minister, party and the UK government by opposing an increased 30% carbon cut. This is deeply undermining to Chris Huhne's efforts to persuade reluctant nations to join the UK, Germany, Spain and others in pushing through the higher target, which they think will benefit Europe's economy.

Of course, lobbying need not necessarily be a "bad thing". In fact, it can be useful in helping to formulate better legislation. But full transparency is essential. The MPs expenses and "phone hacking" scandals have proved once again that sunlight is the best disinfectant.

Lobbying is no different. The Conservative MEPs should be applauded for their openness, and it should be a minimum requirement for all political parties that they publish a regularly updated, standardised register of lobby contacts. But the Tory MEPs need also to heed their own prime minister's advice: that increased ambition on climate change is good for Europe.

Update: The original version of this article mistakenly included the UK Association of Electricity Producers in the list of lobbyists meeting with Martin Callanan MEP to discuss van emissions legislation. This has now been amended.