In the world’s richest football league the trading of players, compressed into two transfer windows, has become a billion-pound whirlwind, involving a flurry of agents whose roles and rewards have never been openly disclosed to supporters or the public. Earlier this year the Football Association injected a sudden gleam of daylight into this market of human talent by publishing a list of the agents, now termed “intermediaries,” who acted on all the deals done by England’s Premier and Football League clubs in the summer of 2015 and January 2016.

New regulations introduced last year, replacing the old licensed agents system, require that anybody advising or negotiating on behalf of a player or club, on the “substantive” terms of any deal, must be registered as an “intermediary” with the FA and reported to the governing body on an official form recording the transfer. The document lists the intermediaries, including familiar big operators such as Jonathan Barnett’s Stellar, Leon Angel’s Base, “super agents” Jorge Mendes, Mino Raiola and Pini Zahavi, who acted in the deals when thousands of players joined clubs, signed new contracts or were sold by English clubs to overseas sides.

Although the document sets out only the names of intermediaries and who they acted for, whether the player, signing club or selling club, giving no detail about the work they did or how much they were paid, its bare essentials nevertheless provide more illumination than ever about how deals are done. In the vast majority, the same agent advised both the player and the club signing him. This “dual representation” of two parties in the same deal is now allowed in English football, if both sides sign an agreement to waive any objection that the agent may have a conflict of interest.

This system was developed in agreement with HMRC, after it won a landmark tribunal victory against Birmingham City a decade ago. The case established that agents who were recorded as having acted only for the club, with nobody representing the player, were in fact the players’ agents and had acted for both parties to the deal. HMRC had challenged this practice, known as “switching,” arguing that the public were being deprived of tax in two ways. First, when a player pays an agent for advising him, the player as an individual pays VAT and cannot reclaim it, whereas a club, as a VAT-registered company, can reclaim the VAT.

Secondly, if a club takes care of the player’s agent’s fee, pays it on behalf of the player, which is common practice across football, that payment constitutes a financial benefit for the player, on top of his salary. So the player must pay income tax on that benefit, invariably at the higher rate of 40%. Where an agent has acted for the club, the fee is paid and there is no such income tax payable on it. HMRC’s successful challenge, arguing that Birmingham had not been “truthful” when claiming the agents acted only for the club, led to a reclaiming of VAT from many clubs which had indulged in the same practice, going back several years.

In today’s transfer swirl, in which the spending of Premier League clubs alone reached £1bn during the year covered by the FA document, it is rare for any player not to have an agent advising on the galactic pay and bonuses, duration and other key terms of a windfall contract in English football. Some may still choose not to. The vast majority of players signing deals are noted in the document as having paid advisers: at Everton, every player had a registered intermediary. At Arsenal, every player who joined or signed a new contract, including senior stars such as Petr Cech, Santi Cazorla and Theo Walcott, together with 25 others, is noted as having an adviser. The only exception was the 16-year-old Vlad Dragomir, who signed from the Romanian club Poli Timisoara.The most noticeable exceptions to that standard pattern were at Chelsea, where among the 28 deals the then Premier League champions concluded, five players were reported to the FA on the official forms as having had nobody representing them in negotiations, while the club instructed an agent in each case.

At newly promoted Watford, the Pozzo family ownership engaged in a rapid series of acquisitions to stock a squad which could stay in the Premier League. Of those, 16 deals are listed in which players joined the club with nobody recorded advising them, while Watford themselves employed and paid an agent to secure these signings. At West Ham, the former captain, Kevin Nolan, agreed a termination of his contract in July 2015 after the manager for whom he previously played at Bolton Wanderers and Newcastle United, Sam Allardyce, left, and Slaven Bilic took over. Nolan is recorded as having agreed this termination with nobody advising him on the substantive terms, while West Ham employed an agent, Kenneth Asquez, based in Gibraltar, to negotiate with Nolan.

Nolan himself is said to have decided that as an experienced player, he no longer needed to pay an agent to advise him, and some sources say that young players making their dream Premier League move might not insist on having anybody to negotiate for them.

Inquiries by the Guardian have discovered that some of the intermediaries listed as having acted only for Chelsea and Watford, in deals to sign players who had no advice, in fact have apparent connections to those players. That makes the record disclosed to and by the FA confusing to the football public, who are given no explanation as to why these clubs chose to pay an agent to secure the deal with a player, while the player himself had no professional advice at all.

There is no suggestion that these clubs or agents have done anything irregular, or that there are any investigations by any authority, including HMRC, into any of these transfer dealings. All three clubs and the agents concerned have emphasised to the Guardian that the deals were reported to the FA exactly as they happened and the correct tax was paid.

The clearest instance of this, where an agent who acted only for the club had an apparent connection to the player being signed, was in Watford’s deal to sign the midfielder Étienne Capoue for £5.7m from Tottenham Hotspur last summer. Mino Raiola, the Monaco-based “super agent,” who delivered this summer’s record £93m transfer of Paul Pogba from Juventus to Manchester United, has been widely quoted in the media describing himself as Capoue’s agent, since before the player moved from Toulouse to Spurs in 2013.

When Watford bought him, Capoue was reported to the FA as having no agent or adviser. Watford, though, stated that Raiola, cited by his full first name, Carmine, was employed and paid to act as the club’s agent.

Confused by the contradiction in this position, the Guardian asked Raiola in a telephone conversation if he is in fact Capoue’s agent. Raiola replied: “Yes.” Asked why, then, he was reported to the FA as Watford’s agent, with Capoue not represented by anybody, Raiola responded: “Take it up with my lawyers if you have a question.”

We did ask that question of Patrice van Oostaijen, who confirmed he is Raiola’s lawyer at the firm Maguire Tax & Legal, in Holland. Van Oostaijen did not then respond to an email asking the question as to why Raiola was declared to have acted only for Watford, and not for Capoue, when the player moved to Vicarage Road.

Of Chelsea’s five signings where the players had no representation but the club paid an agent, three were young players, brought to England from overseas. They were the then 19-year-old Brazilians Nathan and Kenedy, and the US defender Matt Miazga, who was 20. Of the other two unrepresented players one was Chelsea’s own Brazilian first team star, Ramires, then 28, who is stated to have agreed a new four-year contract in October 2015, possibly the most important of his career for earning potential, with no advice from anybody on its substantive terms or pay. The Brazilian midfielder Alexandre Pato, who joined Chelsea on loan from an unhappy spell at Corinthians in January 2016, was the other player recorded as having no advice on the substantive terms of his contract.

In all five of these deals, Chelsea reported on the official records to the FA that the club themselves did appoint and pay agents. Sports Invest, the London-based agency owned by Kia Joorabchian, was paid to act for Chelsea on Pato’s loan deal, and on the £3.5m signing of Miazga from New York Red Bulls.

On the other three deals, including the new contract with Ramires, the Brazilian agent Giuliano Bertolucci was paid by Chelsea to act for it.

Neither Chelsea nor Bertolucci himself responded to questions from the Guardian with an explanation as to why the club needed an agent to negotiate this new contract with a player who had been at the club already for five years, and was not advised by anybody himself. Three months after Ramires signed that four-year contract, in January 2016, Chelsea sold him to the Chinese club Jiangsu Suning; again, the records sent to the FA stated that nobody represented Ramires.

Bertolucci was also appointed by Chelsea and paid an agent’s fee for the £3m signing of Nathan from the Brazilian club Paranaense, and Kenedy, for £6.3m from Fluminese, while neither teenager had anybody negotiating for them and are stated to have themselves agreed the pay, terms and conditions to come to the English Premier League. Nathan and Miazga were immediately loaned to Vitesse Arnhem in Belgium, while Kenedy made four league appearances last season before Chelsea loaned him to Watford.

Chelsea, Sports Invest and Bertolucci, citing confidentiality, declined to discuss why the club appointed agents when these players joined, or what the agents’ role was for Chelsea. Via their lawyers, they emphasised that the details of the deals as published by the FA are correct, that these five players did not have agents or intermediaries advising them or negotiating with Chelsea, and that there was no question about whether the correct tax was paid.

Sports Invest’s lawyers explained that Chelsea sometimes uses Joorabchian’s agency as an intermediary when it has connections with the selling club and also if a number of clubs are competing for a player’s signature. Chelsea appointed Sports Invest to secure Pato on loan because of a “close relationship” with Corinthians, the lawyers said. Joorabchian first came to prominence when he represented a fund, MSI, which financed Corinthians from 2004, then owned the rights to the club’s players, including the Argentinian World Cup stars Carlos Tevez and Javier Mascherano, when they transferred to West Ham United in 2006 .

Joorabchian remained involved with Tevez throughout the controversies over players’ third party ownership and through its subsequent outlawing in English football, including when Manchester City bought the striker outright in 2009 for a fee understood to have been £45m.

Joorabchian is registered at Companies House as the owner and sole director of Sports Invest UK, and his lawyers confirmed: “It is a matter of public record that Mr Joorabchian is a director of Sports Invest and that Sports Invest is involved in Chelsea-related transfers.”

Joorabchian was never licensed as an agent under the old rules; he is now a registered intermediary although he did not personally act for Chelsea on the Pato or Miazga deals. Nojan Bedroud, a former Sports Invest director, is recorded as the agency’s representative acting for Chelsea when they signed Pato. Amir Ali Kohansal, Sports Invest’s representative acting for Chelsea when the club signed Miazga, has a working relationship with the Joorabchian family.

Sports Invest does have an apparent connection with four of the players Chelsea signed who were recorded as having no advice: Nathan, Kenedy, Miazga and Ramires. These players are all listed as Sports Invest’s own clients on the player performance database, Wyscout.

Wyscout, established in Genoa, is a well-respected platform featuring player statistics and film of matches, to which 85 of England’s 92 Premier and Football League clubs subscribe. On it, Sports Invest lists 99 players as its clients, and names Nojan Bedroud, the agent who acted for Chelsea on the Pato loan deal, as its main contact. Others among the mostly Brazilian players listed as Sports Invest’s clients are Chelsea’s David Luiz, Willian and Oscar, Liverpool’s Philippe Coutinho, and Tevez, now playing for Boca Juniors in his home country.

A spokesman for Wyscout said agencies such as Sports Invest themselves actively subscribe to be on the database, and name their own clients. The agencies are on Wyscout only if they have paid for their profile then, they state, “claim” which players they represent, so building a portfolio of clients. Wyscout’s purpose is to ensure the data is reliable, so nobody else can input agents’ clients. Contact details are provided so that clubs are able to contact the named agents if they are interested in discussing the players.

“Any agency which wants to ‘claim’ their clients on Wyscout has to subscribe to the system,” the spokesman said, ”otherwise they wouldn’t have the access necessary. Any players listed under an agency would have to be ‘claimed’ by them.”

The Guardian asked Sports Invest and Bertolucci why the four players, recorded as unrepresented when they joined Chelsea, with the agents acting only for the club, are listed as Sports Invest’s clients on Wyscout. Via their lawyers, Sports Invest and Bertolucci declined to explain. Chelsea said it was a matter for Sports Invest and Wyscout.

Chelsea said they would pass the Guardian’s questions to the players, including why they chose not to have any advice from any intermediary when they negotiated with Chelsea, while the club was represented by Bertolucci or Sports Invest. At the time of writing, no response had been received from any of them.

On the FA’s published document, for five of the players who were not represented when Watford signed them in the summer of 2015, there is publicly available evidence which states that they are in fact clients of the agents named as acting for the club. Besides Raiola’s confirmation that he is Etienne Capoue’s agent, in the cases of three players: Matej Vydra, Valon Behrami and Almen Abdi, the agents reported as having acted only for Watford list the players on their own websites as their clients.

When the Czech striker Vydra signed a permanent deal last July, having been one of the players controversially loaned by Udinese, the Serie A club also owned by the Pozzo family, Watford reported to the FA that they employed Ondrej Chovanec as their agent, with Vydra having no adviser. However, on Chovanec’s own website for his agency, Chovanec Sport, he lists Vydra, who joined Derby County in August, as one of the players he represents.

The Guardian has also seen a copy of the official filing for Vydra maintained by the Czech Football Association in a register of all its members. That also records Chovanec as Vydra’s agent. Chovanec did not respond to emails asking him about this apparent contradiction, and when contacted by telephone said that he does not talk to the press.

When Watford signed the Swiss midfield player Behrami for £2.5m from Hamburg, Nikola Damjanac, a Serbian former goalkeeper, is recorded as having acted exclusively for Watford, with the player unrepresented by any adviser. On Damjanac’s website for his agency Lian Sports, Behrami is featured in the list of players represented. News is also prominently displayed about him, most recently his role in Switzerland’s 2-0 victory over the Faroe Islands in last month’s World Cup qualifying match. Damjanac did not respond to emails asking about this discrepancy, nor to telephone calls to numbers listed for him on a register of Serbian agents.

When Behrami’s fellow Swiss midfielder, Abdi, signed a new three-year contract in July 2015, he had already been at Vicarage Road for three seasons, having in 2012 been another of the players loaned from Udinese. The FA document shows that Watford nevertheless employed and paid an agent to negotiate for the club the new contract with Abdi, who is stated not to have been advised. The agent the club employed was Dino Lamberti, founderof the Fair Play Agency based in Zurich. On its website, Abdi, who has since joined Sheffield Wednesday, is listed prominently as a client

Abdi’s official Twitter account states that it is jointly managed by Fair Play Agency; Lamberti’s agency is listed as the contact for Abdi on his Facebook page, and on the agency’s own Facebook page it lists Abdi’s. Lamberti did not respond to emails or telephone messages left at Fair Play Agency’s Zurich office, asking why he was reported to the FA as having acted only for Watford on the negotiation of Abdi’s new contract last year, while the player was unrepresented, when he lists Abdi as one of his clients.

The Lithuanian goalkeeper Giedrius Arlauskis, who joined Watford from Steaua Bucharest last summer and has since been loaned to Espanyol, was also recorded as having negotiated the deal himself to join Watford in the Premier League. The agent employed and paid to act for the club was Leonid Istrati. On the Soccer Assocation database, Istrati’s iFootball agency lists Arlauskis as one of its clients

In a statement, West Ham said: “FA registered intermediary Kenneth Asquez acted on behalf of the club to assist with the negotiation of the termination of Kevin Nolan’s West Ham United contract, which was declared on the relevant FA Forms. To the club’s knowledge, Kevin Nolan has never been represented by Kenneth Asquez.

“Furthermore, when Kevin joined West Ham United from Newcastle United in 2011, neither he nor the Club were represented by an FA licensed agent.”

The FA declined to comment on apparent relationships revealed between some of these agents and players, but indicated it believes the public naming of the intermediaries who acted in all deals is a progressive move, allowing more information to be known. “Transparency of transactions is an important part of the new regulations,” an FA spokesman said.