The Premier League premium is £20m - and that worries European clubs

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 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.