MPs have been accused of failing to provide "sufficient" transparency after a Sky News investigation struggled to uncover basic details about who is behind major donations.
Among the top donors to individual politicians are companies where little detail was provided in the MPs' declarations about who they are, who is in charge and where they are based.
When asked for comment, some of the MPs concerned were reluctant to discuss the details.
In one case, Sky News discovered that nobody had heard of a company donating hundreds of thousands to Labour MPs on a visit to its registered address, while the office of another company that donates to 24 Tory MPs was shut and apparently out of action.
Hannah White, the director of the Institute for Government, told Sky News that MPs should be prepared to answer questions about the donations they accept.
It follows an investigation as part of the Westminster Accounts that examines two companies ranked in the top 20 list of donors to individual MPs.
The declared donations provide the public with little information about the true source of the money.
MPM Connect Ltd is the third-biggest donor to MPs since the last general election. The only organisations that have given more to individual politicians in that period are the trade union giants Unite and GMB.
The company has no staff or website and is registered at an office where the secretary says she has never heard of them.
The £345,217 of donations that MPM Connect has made since the end of 2019 went to three Labour politicians.
Yvette Cooper, the shadow home secretary, has received £184,317, former mayor of South Yorkshire Dan Jarvis £100,000 and shadow health secretary Wes Streeting £60,900.
MPM Connect's entry in the Companies House register lists two directors - recruitment mogul Peter Hearn and Simon Murphy, the entrepreneur behind the redevelopment of Battersea Power Station.
The company's accounts do not disclose where it receives its funding, what it does or why it donates so heavily.
When Sky News went to the office in Hertfordshire, where the company is registered, the receptionist in the building denied any knowledge of MPM Connect.
She told Sky News she did not recognise the names of the two directors.
"We'd rather not speak to you," she said, before closing the door.
Mr Hearn and MPM Connect were approached for comment, but no response has so far been received.
Sky News asked each of the MPs to provide an explanation or comment in relation to who was behind the donations and why the money had been given to them.
How did the politicians respond?
Yvette Cooper's office initially issued a response which they said could not be quoted.
However, after Sky News published this story, a spokesperson for the shadow home secretary said: "MPM Connect is an investment company in the employment sector owned by Peter Hearn, a UK businessman and long standing Labour supporter, and as has been reported many times, Mr Hearn kindly donates money to fund Yvette's office staff and has done so for many years.
"It has all been fully declared and compliant with all the rules. Like lots of companies, MPM Connect is registered to their accountants office, as is made very clear in its Companies House entry."
Prior to publication, Mr Streeting also only offered a short response saying all donations had been declared in the proper way.
This afternoon a spokesperson issued a new statement, saying: "Peter kindly funds staff for Wes's office. Wes is proud to have successful business people supporting the Labour Party in our campaign to win the next election and give Britain the fresh start it deserves. This has been declared in the proper way in accordance with the rules."
Mr Jarvis said all his donations support his work as an MP.
Electoral Commission records show that over the past 20 years, Mr Hearn has made a number of significant donations to political parties. These have almost all been to the Labour Party, though he made a £10,000 donation to the Conservative campaign for the seat of Poplar and Limehouse before the 2010 general election.
In 2015 he spent £100,000 on Ms Cooper's unsuccessful campaign for the Labour leadership, and Rushanara Ali's deputy leadership bid, before turning his attention to Mr Jarvis in an attempt to dethrone Jeremy Corbyn and his deputy Tom Watson.
Broadband provider donated money to Tories
Another large donor where the public declarations leave ambiguity over the ultimate source of the funding is a little-known broadband provider from Blackburn.
IX Wireless has channelled more than £138,000 of campaign donations to Conservative MPs since 2019, despite only having two staff members, one of whom lives in the United Arab Emirates.
One of those politicians who received money from IX Wireless was Christian Wakeford, who was a Conservative MP at the time before defecting to the Labour Party in January 2022.
He told Sky News he had no "understanding or details as to who they were, what they were doing or what they wanted" when the donation was made.
Mr Wakeford said he had been told by Sir Jake Berry, a senior Tory MP and former party chairman, that there was a block of money from a donor available and to write an application for the funding.
"We'd put those applications in," he said, "and we'd find out a month later whether those applications were successful and that the monies were going to our local Conservative association."
"It was only at that time we were told the money had come from IX Wireless," Mr Wakeford said. "I'd never heard of them. The first I'd heard of them was the email telling us."
Mr Wakeford said he now knows more about the company.
Sir Jake was approached for comment but did not respond.
On a visit to the headquarters of IX Wireless, Sky News found the office empty with flooded floors.
Standing outside the company's front door, Sky News called IX Wireless and spoke to someone who said they were a receptionist.
She confirmed that the address was correct, but would not say that she was inside the headquarters. After placing the call on hold for several minutes, she declined to answer any questions.
Founded by the entrepreneur Tahir Mohsan in 2017, the company was a successor to Time, a successful British personal computer brand in the 1980s and 1990s.
In 2005, Mr Mohsan's computer empire abruptly collapsed with £70m in debts, making 1,500 people redundant.
Thousands of customers had to fight for refunds on products already ordered.
Shortly after the company failed, Mr Mohsan left Britain for Dubai in the UAE.
He has since turned his attention to installing broadband in the North West of England, receiving £675,000 of government funding to roll out high-speed internet in less connected areas of the country.
The company connected 500 premises between August 2018 and June 2020, according to government data seen by Sky News.
IX Wireless and Mr Mohsan did not return repeated requests for comment.
Ms White, of the Institute for Government, told Sky News that MPs needed to be more forthcoming about the money they were taking.
"I think there's a bigger question here... is that transparency actually sufficient?"
Ms White questioned whether it was appropriate for politicians to avoid questions from members of the press and the public over the identities of donors.
"If an MP is asked for more information, should they feel that actually that is something that they're willing and able to give? Do they actually know the answer to some of these questions if they've taken money from a company that they don't necessarily know how that is funded? I think that's actually quite important," she said.