Transparency campaigners have hailed an investigation into the flow of money into Westminster as a “wake-up call” for British politics.

The months-long investigation by Sky News and the Tortoise news website has resulted in the launch of a new database of political donations and MPs’ outside earnings.

The database, called the Westminster Accounts, compiles records from the MPs’ Register of Interests, the Electoral Commission and other official registers and aims to provide a comprehensive picture of the financing of British politics since the last election.

Duncan Hames, director of policy at Transparency International UK, said the database would “empower” members of the public to ask questions about the donations their MPs were receiving.

Speaking to the PA news agency, he said: “We’re used to trawling through all sorts of registers. This puts it very easily at the fingertips of everyone and enables us to move on from formal declarations and transparency returns to some real accountability.”

The investigation has already raised questions about the true source of political donations from companies.

Mr Hames warned that donations by companies made it harder to see who was really funding UK politicians.

He said: “For the most part, this isn’t the big multinational companies that you’ve heard of. More often than not, these companies are simply mechanisms by which very wealthy people organise their wealth and their assets.

“It’s not like you’re looking on the register to see if McDonald’s has been funding a political party – it’s a company that’s in all likelihood owned by a couple of people and it’s really them that are giving money to the politicians.”

He added: “The public has a right to know, and if who is funding their politicians is shrouded behind layers of company transactions then they don’t really know.”

Susan Hawley, executive director at Spotlight on Corruption, echoed Mr Hames’s comments, saying: “This should be a real wake-up call to the UK political establishment to get serious about ensuring parties conduct proper checks on donations and are fully transparent about where the money is coming from.

“More fundamentally, we have to have a serious public debate about the undue influence that donating to political parties allows, and how that distorts democratic decision-making.”

Both Rishi Sunak and Sir Keir Starmer said they welcomed the publication of the Westminster Accounts database.

Speaking to reporters in West Yorkshire on Monday, the Prime Minister said: “I think transparency is really important for the healthy functioning of democracy, it’s absolutely right that there’s disclosures around donations and outside interests.”

On Sunday, the Labour leader told Sky News’ Sophy Ridge: “I think we’ve got some of the strongest rules in terms of what we have to declare, but the more transparency the better, so that everybody can see exactly what has been declared and ask whatever questions they want to about it.”

As well as political donations, the Westminster Accounts identified the MPs earning the most from second jobs, with former prime minister Theresa May coming top of the list.

Mrs May has received £2.8 million in payments and gifts since December 2019, mostly in the form of speaking fees paid to her private office.

Former attorney general Sir Geoffrey Cox was the second-highest earning, receiving £2.1 million, mostly from his legal work, while Boris Johnson has received £1.2 million since December 2019.

Mr Johnson’s payments include more than £1 million in speaking fees earned since he left Downing Street in September.