Now in its 20th year, the Deloitte study ranks the world's richest football teams by turnover during the 2015-16 season and this year's top three of United, Barcelona and Real is the same as the first edition in 1997.

Real, who had topped the list for 11 years, were beaten to second place by their La Liga rivals by just €100,000.

United, on the other hand, have surged ahead of the pack, becoming the first football team to earn more than £500 million in a season -- the club's total revenue of £515m is almost £50m more than Barcelona and Real generated.

The report's author Tim Bridge told PA Sport: "You can't really look past Manchester United returning to the top spot and it is because of their ability to make commercial deals that are way ahead of their peers.''

Citing United's record-breaking kit and sponsorship deals with Adidas and Chevrolet, Bridge said Europe's other super clubs are now using the Old Trafford outfit as a benchmark in their own negotiations with commercial partners.

United's 2015-16 earnings were also boosted by a return to the Champions League, which meant more broadcasting and matchday revenue.

But they were not the only Manchester club to enjoy off-field success as City climbed to fifth in the money table. Thanks to their growing commercial strength and run to the Champions League semifinals, they earned £393m.

One spot higher than City in fourth are Bundesliga giants Bayern Munich, who bring in double what closest domestic rival Borussia Dortmund (11th) earn. French champions Paris Saint-Germain fell two places to sixth.

The next three places are filled by Arsenal, Chelsea and Liverpool, non-movers but all setting new club records for revenue.

Spurs are the next best-placed English outfit in 12th, on £209m, with West Ham and Premier League champions Leicester new entrants in the table at 18th and 20th, respectively.

Juventus heads the list of four Italian teams, in 10th place on €224.5m, followed by AS Roma (15th at €218.2m), AC Milan (16th at €214.7m) and Inter Milan (19th at €179.2m).

The fact they Leicester and West Ham sandwich the once-mighty Inter Milan in is testament to the Premier League's financial muscle and Serie A's decline. The Milan club are one of 10 ever-presents in the top 20 since 1997, but are projected to fall out of the rich list for the first time next year.

A large reason for that will be the arrival of several more Premier League clubs buoyed by the first year of the new domestic TV deal in 2016-17 -- a source of income that has caused alarm around Europe, particularly as it is immune to the vagaries of the foreign exchange market.

This year's report sees eight English clubs in the top 20, matching a record achieved nine times before, and 12 in the top 30, which is actually a sharp fall from last year's 17.

Bridge puts this down to strong commercial performances from clubs such as Fenerbahce, Galatasaray and Lyon, and Spain's more equitable television deal helping the likes of Atletico Madrid. But he believes the Premier League's broadcasting millions will see as many as 16 English teams in the top 30 next year.

This, however, is not the dominance some have predicted for the Premier League and Bridge said the uncertainties of the post-Brexit vote era could also hinder English sides' earning power.

Deloitte based this report's figures on an average exchange of £1 = €1.33.7, but the current inter-bank rate is £1 = €1.15.

"Despite the Premier League's new TV deal, I think next year's list will be a tight, three-way scrap between United, Real and Barca,'' said Bridge.

Leicester's strong run in the Champions League could see them climb into the top 15 next season, particularly if they can get past Sevilla in the round of 16 this year.

The overwhelming message from the report, though, is that Europe's elite clubs are separating themselves from the field, a trend recognised by last week's financial update from UEFA.

In the foreword to that report, UEFA president Aleksander Ceferin said the governing body must take note of the "increasing concentration of sponsorship and commercial revenue among a handful of clubs."

This can also be seen in the Deloitte study, with Manchester United's turnover in 2015-16 being four times greater than Leicester's. The multiple from 20th to first in 1997 was closer to three.

And looking further ahead and afield, the only possible non-European candidates for the top 20 in 2030 are most likely to come from China, although their richest clubs now only earn a tenth of what Bayern presently make.