Iliman Ndiaye (£65m), Savio (£75m) and Carlos Baleba (£70m) moved between English clubs for fees which could not be achieved outside the Premier League. The old adage used to be that English players came at a premium. Now that appears to simply apply to a player already in the Premier League.

As English football set a host of new records for spending in the summer window, the average spend on a player signed from another Premier League club was £39.4m - almost double the £20.2m spent on those arriving from abroad. Kieran Maguire, professor of football finance at the University of Liverpool, calls it "a Premier League tax". It is part of a growing trend which has seen Premier League teams become increasingly comfortable with selling to each other, even rivals.

While more total spending is done with clubs outside of England, the proportion of big-money domestic deals is now outstripping overseas transfers. Only the European elite can now compete with Premier League clubs, and player profits are key when it comes to recycling money to keep in line with the financial rules.

Spending patterns for Premier League clubs are not just about the fee, but who the clubs are choosing to do business with. Take a look at the high-value deals, worth £40m or more, which have doubled this summer from two years ago. In 2024-25 there were 13 such deals, this summer there were 27.

More striking is the breakdown of these transfers. Two years ago, there were seven transfers worth £40m or more done with teams on the continent. Only six were completed between Premier League clubs. Now look at what has changed. This summer there were nine deals worth £40m or more with European clubs. But between clubs in England, it has trebled, from six to 18.

The total spend across all domestic transfers has more than doubled, too. Maguire told BBC Sport that one reason is English clubs now scout players from abroad so extensively that they are signed much earlier, and made into Premier League players. "We've got a new tranche of clubs, sort of the algorithm kids, who are recruiting from the international markets," Maguire said. "They're bringing players to the Premier League, and then the Big Six clubs are signing the best players."

On such example is Carlos Baleba, who Brighton signed from Lille three years ago for £23m and last week sold to Manchester United for £70m. "It has effectively created a recruitment area, sort of a petri dish, to determine which of the overseas players can deliver in the Premier League, and then it's a win-win for all the parties," Maguire added.

But that only tells part of the story. There are also the transfers which look like they could only happen in the Premier League. Would a European club have given Manchester City the £75m Tottenham spent on Savio? Or paid Everton £65m for Iliman Ndiaye? What about the £85m West Ham received from Spurs for Mateus Fernandes?

As if to underline this, only seven signings of £40m or more were made this summer by European clubs, from another on the continent, all by Barcelona, Bayern Munich and Paris St-Germain.

Trevor Watkins, the former Bournemouth chairman who now works as a sports lawyer, told BBC 5 Live Breakfast that the Premier League almost operates within its own bubble. "The revenues dwarf what other leagues generate," Watkins said. "And what you see this year is a lot of deals between clubs in England. A lot of money going down to lower leagues, but also between Premier League sides because, to be honest, they're probably the only ones that will pay the wages or pay the fees."

The transfer market appears to have become a game of spreadsheets where it is almost impossible to value players against each other. The reason is simple, but the explanation more complicated. Profit on a transfer is in some ways more significant than a player's worth in saves, clearances, assists or goals. Because profit enables reinvestment in the squad.

Let's try to set out how it works. Elliot Anderson cost Nottingham Forest £35m from Newcastle, and they sold him for £116m. But that is not a profit of £81m. The original transfer fee is averaged over the length of his Forest contract, and when he moved to Manchester City, around £21m was left on the books. Under the Premier League's new squad cost ratio (SCR) rules, that is a profit of £95m which is averaged over three years, at £31.67m for Forest.

Clubs can no longer sell a player for a one-hit quick fix - either to boost spending power in one window or to avert breaches of the financial regulations. Why does this matter? It makes it even more important for clubs to generate high transfer fees, to get a higher profit average for SCR - which itself is calculated over one season. But SCR undoubtedly benefits the biggest clubs with the greatest financial power.

The 'Big Six' - Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham - with their commercial revenues on a completely different scale, spent £1.658bn on players. "Those clubs have future-proofed themselves by trying to generate more income," Maguire said.

Spurs is a classic example. Spurs now have a multi-function, multi-sport stadium, of which the football club is the biggest part. "It is a reward for those clubs that have expanded their stadiums, or thought outside of the box in terms of trying to generate additional revenues."

For the other 14 clubs, who in total spent £1.833bn, player trading is crucial. Between them, Aston Villa and Newcastle completed five deals worth £40m or more, but only after they brought in hundreds of millions of pounds from player sales.

Elliot Anderson's move to Manchester City is worth £31.67m a year to Nottingham Forest in transfer profit. If Premier League clubs are spending more of their money between themselves, that means less is flowing onto the continent. But there are fears that this will still act as an inflationary trigger for fees and wages across the continent.

On Wednesday, Javier Gomez, La Liga's corporate general director, criticised the "loss-making model which is an issue exclusive to the Premier League". "It has other consequences," Gomez said. "It inflates the entire sector - it inflates the Premier League, the Bundesliga, the French League, and eventually us as well."

Some of Europe's traditionally bigger teams have already found themselves no longer able to compete with the top teams in the Premier League. "With the exception of some of the global brands within football, and I think you'd look at Real Madrid, Barcelona, PSG and Bayern Munich, the Premier League can outspend anyone and everyone," Maguire said.

"We've seen that in the recent Deloitte Money League, external with 14 teams from the Premier League in the 30 biggest teams in world football." Real, Barca, PSG and Bayern are the top four on that list with Liverpool leading the six English clubs that fill out the top 10.

Andre Villas-Boas, the president of FC Porto, told BBC Sport that the Portuguese club has had to step up their scouting efforts instead of getting into bidding wars they cannot win. "For Porto, it means we are competing for talent not with Man City or Liverpool but with (the likes of) Coventry and Brentford, without any disrespect," Villas-Boas said. "The fact that they have this spending power makes it difficult for us. "The Premier League is set apart from all the rest, which means English clubs are becoming more and more dominant of European competitions."

Aston Villa and Crystal Palace won the Europa League and Conference League respectively last season, while Arsenal were beaten by Paris St-Germain in the final of the Champions League.

The Premier League's transfer spending is the bubble which just refuses to burst. And it risks creating further inequalities in European football.

This video cannot be played. Villas-Boas says Premier Legue spending makes it 'difficult' for other European leagues. A record-breaking transfer window. Ranking the most game-changing transfers in Premier League history. How Everton's deadline day debacle leaves owners facing fan mutiny.