MP Gisela Stuart has an undeclared directorship. YouTube/Parliament.UK/Still Incorrigible Nearly 2,800 active company directorships are held by politicians in Westminster, according to a book published on Thursday that sheds light on the financial interests of members of the houses of parliament.

"Parliament Ltd: A journey to the dark heart of British politics", authored by journalist Martin Williams, found that MPs and lords are directors in 2,465 companies with combined revenues of £220 billion and a combined workforce of 1.2 million people.

A rough-cut analysis by Williams suggests that around 40% of these directorships are not fully declared on parliament's official Register of Members' Financial Interests. Another 6% were only partially declared, and another 3% were declared with major errors, such as incorrect spelling of company names.

There are currently around 1,450 members of the houses of parliament, with 650 MPs and around 800 lords.

There is no suggestion in the book that any of the MPs identified have broken any rules. However, the data, surfaced with the help of London tech startup DueDil, includes several potentially controversial directorships.

Lord Evans of Watford, for example, did not declare his directorship in Strategic Matters LLP, a partnership business which sponsored the Kazakhstan-US convention in 2014, while pro-Brexit campaigner MP Gisela Stuart holds an undeclared partnership interest in a wealth management firm offering tax planning advice to high-net-worth. The latter has already caught the attention of BuzzFeed.

"I definitely think there is a huge issue with money and business in parliament," Williams told Business Insider ahead of the book launch. "With this book and I’m hoping to shed some light on that and let people know about it.

"The problem is across all parties. I’ve tried to not be too party political in this. It’s a statement of fact that conservative politicians probably have more involvement with big business than labour MPs but that doesn’t make labour MPs guilt free of anything."

William's, who has written for the Guardian and Private Eye, notes that not all of the directorships he discovered need to be declared by law. Those that do are the ones that could influence voting decisions or the way MPs and lords speak in parliament.

"It would be wrong to suggest they would have to declare all of these things but the point I’m making in the book is that there’s no way of checking unless you do a massive project like we've done," said Williams.

In order to determine which cases should have been declared, each one would have to be individually investigated by the parliamentary commissioner, Williams said.

Surfacing the data

Williams asked DueDil, a company with a tool that combines sources of company information, to compile a data set listing every UK company directed by an MP or a Member of the House of Lords.

DueDil data scientists used the DueDil tool to cross-reference specific names — including different spellings and aliases — with known UK company directors, producing what it claims is an accurate list of companies linked to politicians.

DueDil cofounder and CEO Damian Kimmelman said in a statement: "By using DueDil’s ability to provide insight into vast datasets, Mr. Williams has been able to put together the most comprehensive analysis ever of UK politicians’ business interests. This feat highlights the power of DueDil to bring more transparency to company ownership, helping any kind of business find complete, accurate information."