There will always be some rotten apples, of course. No matter how honest and hardworking most politicians may be, some will always fall short. But if Westminster were more transparent, at least it would be easier to keep track of the finances. The truth is, however, that authorities actively help MPs to keep things under wraps.

How many of our representatives stand to gain directly from the decisions they push through? How many could profit from NHS privatisation, housing policies or even military action? We have no idea.

With the help of business intelligence firm DueDil, though, I began building a database of all the UK companies that had MPs and peers on their board of directors.

It was a mammoth task – and never done before – but the results were staggering. We identified about 2,800 active directorships, linked to almost 2,500 companies. Together, these firms employ at least 1.2 million people – equivalent to one in 20 of the UK’s full-time workforce. And they bring in more than £220bn of revenue annually. …

… This doesn’t necessarily mean MPs have broken any rules – although some have. But that’s exactly the point. The system itself fails to enforce transparency in politics. That’s why David Cameron can legitimately claim he didn’t break any rules when he failed to declare his stake in his father’s offshore Panama fund. The system allowed him to dodge transparency. Indeed, often the rules actually force MPs to hide information. One line says: “Members should not specify the value of the shares, or the percentage of shares in a company that are owned.”

The register of interests contains some of the most crucial information to our democracy. It doesn’t stop corruption in itself – but it does give a clue about whether MPs are speaking on behalf of voters or a private company they work for. Yet this vital document is scrutinised by no one. MPs’ declarations are only ever investigated if other people make an official complaint about someone. The whole thing is based on trust. And the result is that tons of stuff gets missed off – whether intentionally or not. …

… Because the system fails on transparency, it’s easy to see how financial controversies can brew undetected; not noticed until it’s too late. It’s a similar story with expenses. After the 2009 scandal we were promised a complete reform, yet the stories keep coming. For instance, one set of documents I found reveals how a peer claimed nearly £9,000 for a business-class return flight from New York, just to make a four-minute speech in parliament. Why had this not been discovered before? Because the files were buried in an archive, only retrievable through protracted freedom of information requests. What’s more, many of the worst abuses of the 2009 scandal would still be completely untraceable under the current system because key details are often redacted by the authorities.