Boris Johnson has said plans by top football teams to create a breakaway European Super League would "create a kind of cartel".
The Prime Minister threatened to find a legislative solution to block plans for 12 clubs - including the Premier League's so-called "big six" - to join a controversial new European competition.
Speaking at a Downing Street press conference, Mr Johnson said: "Be in no doubt that we don't support it... the creation of this European Super League.
"I think it's not in the interests of fans, it's not in the interests of football.
"How can it be right to have a situation in which you create a kind of cartel that stops clubs competing against each other, playing against each other properly, with all the hope and excitement that gives to the fans up and down the country?
"I think it offends against the basic principles of competition."
Mr Johnson warned that the Government would "seek a legislative solution" if necessary to protect these principles of competition.
Liverpool, Manchester United, Man City, Tottenham, Arsenal and Chelsea have all signed up to the plans, alongside top teams from Italy and Spain.
However the move has triggered an explosive backlash from fans, as well as football authorities in England, plus Uefa and Fifa.
Mr Johnson said it was wrong that historic British clubs were being turned into "international brands and commodities".
He said: "Football was invented and codified in this county.
"It is one of the great glories of this country's cultural heritage. These clubs, these names, originate from famous towns and cities in our country.
"I don't think that it is right that they should be somehow dislocated from their home towns, home cities, taken and turned into international brands and commodities that just circulate the planet propelled by the billions of banks without any reference to fans and to those who have loved them all their lives."
Mr Johnson insisted the British Government would legislate if there was no other way to stop the plan.
"That remains something that we will bring to the forefront if we have to," he said.
"What we want to do first of all is back the FA, back the Premier League, and hope that we can thwart this proposal before it goes very much further."
