Lobbyists will lobby, so the argument goes, but it's all above board and we the public don't need to worry about it. Today's investigation by the Bureau of Investigative Journalism with The Independent shows why that's not true.

It is healthy in a democracy for elected politicians to make decisions based on evidence and argument – and if some of that evidence and argument comes from vested interests that is not, in itself, a bad thing.

But the problem comes when the role of those vested interests in formulating policy is kept secret both from the public and even sometimes the politicians who are being lobbied.

This is laid bare by the Bureau's investigation with The Independent. It shows the inner workings of lobbying firms like Bell Pottinger who use former politicians to get access to their old colleagues – often at unrecorded "social events" without civil servants present – to push their clients' agenda.

As Tim Collins, the managing director of Bell Pottinger Public Affairs and former Tory MP put it in his pitch: It is about "inviting them [clients] into political circles, to dinners, to social events, to opportunities to engage with a lot of the key decision makers."

One could argue that this might be fanciful boasting. But separate research by the Bureau has uncovered evidence of an unrecorded dinner between Eric Pickles and key Bell Pottinger clients at a five-star hotel, organised by the firm. When asked why he had not declared the dinner Mr Pickles claimed it was a "private" engagement.

We don't know how many other dinners there have been, and how many other politicians have been involved. But we now know there is an intent and a precedent – and that should concern the public – because it is in the public interest.

The other area of concern highlighted by the investigation is the way in which lobbying firms are now using the internet to manipulate and enhance their clients' interests.

Before now, not many people knew of the "dark arts" of changing Google rankings, or of setting up apparently independent blogs to promote their clients' interests, or of altering Wikipedia pages. But now we do – and it should concern us all.

Finally the investigation exposes the type of clients that lobbying firms, such as Bell Pottinger, are prepared to take on.

Uzbekistan may have a truly awful human rights record but – unlike some lobbying firms we contacted – that did not put off senior executives from pitching hard for the business.

They made clear that in order to be effective they would need to be able to show change happening – but it didn't need to be rapid. And Bell Pottinger's previous work for Belarus, Bahrain and Sri Lanka proves it is not opposed to doing business with states with dubious records.

These problems could be addressed in three reasonably simple ways.

The first is a register of lobbyists – so the public and the politicians know who is representing who.

This would include who the lobbyist is, who they work for, the area of policy they are hoping to influence and which government department or agency they are trying to influence.

The second is a statutory code of conduct for lobbyists that addresses what is and what is not acceptable behaviour.

Last, but not least, politicians must be obliged to register their meetings with lobbyists – be they in an office, a restaurant or a reception – when clients' interests are raised.

This is not without precedent. The hacking scandal has rightly resulted in ministers detailing their dealings with senior media executives and this should now be extended to lobbyists.

As David Cameron rightly predicted, lobbying could become the next great scandal to engulf the political system.

It is within his power to stop the scandal in its tracks. Will he?

* Caught on camera: top lobbyists boasting how they influence the PM
* The Sting: The fake 'Asimov Group' meets Bell Pottinger
* The Transcript: 'David Cameron raised it with the Chinese Prime Minister'
* We wrote Sri Lankan President's civil war speech, say lobbyists
* Vicious dictatorship which Bell Pottinger was prepared to do business with
* Oliver Wright: Vested interests are entitled to argue their case, but it must be in the open
* Andrew Grice: Plenty of talk about cracking down on lobbying – but still there's no action
* Leading article: Evidence of a lobbying industry out of control