The "scandal" of MPs' earnings from second jobs and donations exposed by Sky News' Westminster Accounts project "needs to end" through "root-and-branch" reform, the SNP has said.
The party's Westminster leader Stephen Flynn told Sky News' deputy political editor Sam Coates that the findings of the investigation should "ring alarm bells for everyone" and demonstrate that a "complete overhaul" of the rules is required.
Describing the situation as "not acceptable", Mr Flynn said "everything needs to be on the table" when it comes to reform, adding: "We need to have transparency in public life."
On Sunday, Sky News and Tortoise Media launched a new database of MPs' outside earnings - the first time they have all been collated in one place.
According to Sky News' analysis of the MPs' register of financial interests, 38 MPs have taken on second jobs where the ultimate party paying them is unclear.
While 14 MPs have been given more than £250,000 each towards their campaigns and causes.
The investigation also discovered that nobody had heard of a company donating hundreds of thousands to Labour MPs on a visit to its registered address.
Mr Flynn told Sky News that the project has highlighted that "the Westminster system is broken and corrupt", with MPs earning millions outside of their parliamentary day jobs.
After asking Rishi Sunak a question on former prime minister Boris Johnson's outside earnings at PMQs earlier today, Mr Flynn has now written to the current PM calling for him to introduce robust legislation to tighten the rules.
The SNP's Westminster leader's demands include:
• a ban on "dark money donations"
• a block on MPs from taking second jobs that involve "a considerable time commitment or conflict of interest"
• tightened restrictions and full transparency on outside earnings
'This is the expenses scandal all over again'
Mr Flynn told Sky News that the revelations uncovered by the Westminster Accounts project will be "of huge concern to the public".
"We are all public servants, we serve the public - and if the public don't know why we are doing what we are doing or who is funding us that is deeply concerning," the SNP's Westminster leader said.
He continued: "But if we are going to have transparency in British politics, we need to get to the bottom of this and ultimately Westminster needs reform."
Mr Flynn added: "And we should also broaden that discussion out to whether MPs should be spending as much time as they are on second jobs when, in reality, they are members of parliament there to legislate.
"It is pretty clear cut to me that we should be putting out duties in parliament first."
Mr Flynn said he was "sceptical" that change will happen, describing Mr Sunak as being "ambivalent" to the idea earlier on Wednesday.
In a statement, the SNP's Westminster leader added: "This is the MP expenses scandal all over again."
Senior politicians react to Sky News' Westminster Accounts project
Earlier this week, the prime minister said there was a reason that "rules and regulations" are in place surrounding donations to MPs after the Westminster Accounts project launched.
Mr Sunak 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. And transparency is a good thing, and I fully support it."
However, he did not answer when asked whether it was right that some MPs are being given six-figure donations.
Chancellor Jeremy Hunt told Sky News that the information will help people make more informed decisions at the ballot box.
"People should know what income their MPs are receiving, what funding they have for their political campaigns. I think it's really helpful that you have put that information together so people can make a judgement at the ballot box as to whether MPs are behaving the way they want," he said.
Asked about the prospect of reforms, he insisted the UK has one of the most transparent systems "in the world".
'It wouldn't take much to just sort this out'
But the chair of parliament's ethics watchdog said the Westminster Accounts project has shown that MPs should be forced to exercise more "due diligence" over donations.
Praising the investigation, Lord Pickles told Sky News that MPs should have to know and declare a named individual as the originator of a donation, even if the funds come from a company.
"It wouldn't take very much to just to sort this out," said Lord Pickles, who is the chair of the Advisory Committee on Business Appointments.
He added that it "wouldn't be unreasonable to put together some guidelines for MPs to be able to answer some just very basic questions".
While Labour's Chris Bryant posted on social media: "I welcome Sky News and Tortoise's work making information that is already in the public domain more readily accessible."
Earlier today, Sky News' Westminster Accounts project revealed all-party parliamentary groups (APPGs) have received over £20m worth of funding from external organisations since the 2019 general election, with registered lobbying agencies dominating the ranks of biggest benefactors.
APPGs are informal interest groups of MPs and peers that facilitate cross-party work on an issue, a country or a sector, but the chair of one of Westminster's ethics watchdogs has told Sky News they could represent "the next big scandal".