These schoolfriends quit their jobs in finance to bust the banks' pay cartel
Since setting up Emolument, the pay data company, with schoolfriend Olivier Beau de Lomenie in 2012, he's had to deal with some angry calls from former clients.
Emolument works by crowdsourcing data on salary and bonuses by industry and geographical location.
Users upload their information, getting a report on where they place in their job market in return, even compared to alumni from the same university.
Around 94,000 have signed up so far.
Banks, which have discouraged employees from sharing pay information, aren't hugely happy.
"I had a call from one of my friends in HR in Nomura, who I did some work for when I was a consultant, and their global head of comms had been very upset because Nomura had been top of the league table for pay," Drewry said in an interview at the company's London office.
"I said: 'Dude I'm sorry, you're not our client, if that's what the crowd says, that's what the crowd says'.'"
Accuracy and data security are key to the business, according to Chief Operating Officer Alice Leguay, herself a former banker.
"Getting paranoid bankers to give us their pay details is a matter of trust," she said. "We're hearing of bankers walking into their annual review with their Emolument report printed out, and saying 'well this is where the market is.'"
Getting the pay data into a shape where it's comparable with others is also a challenge.
And part of why the founders feel the business is marketable.
While other sites such as Glassdoor have approximate pay scales, Emolument has figured out a way to match up the data between banks and employers, even if they have different job titles for the same thing, making the report more specific to the user.
For example, banks may use the same terms, such as associate and senior vice president, but for different levels of seniority.
"How do you classify these jobs so they make sense?" said Olivier Beau de Lomenie, the chief technology officer and a former architect of Ocado's online supermarket system. "That was one of the hardest things."
Emolument has raised money three times. It's brought in a total of £1.4 million ($2.2 million) in investment, via a combination of private investors and the so-called seed enterprise investment scheme, a tax-efficient government programme.
So far Emolument is still figuring out a revenue model. It's sold specialised aggregated data reports to recruitment firms, but the company's founders only drew their first salary three months ago. At the moment, the focus is on gaining critical mass.
"The board is absolutely committed to letting us do our job and build the crowd," said Drewry. "It's like LinkedIn. It didn't make any money for six years. Unless you have a critical mass of data, you're not going to be able to sell anything of value. At the moment, we're not trying to monetize the user. We may or may not offer a premium service down the line as LinkedIn does."
Banks have "a cartel mentality," over controlling pay, especially at a junior level," said Drewry, which they enforce by telling bankers they can't talk about it.
"There is this taboo element that has to be lifted. You can price compare anything in this world, but you could not compare one of the most important things in your life - which is how much you earn."