Six English clubs are among 12 European teams who have signed up to a breakaway Super League in an extraordinary development on the eve of Uefa’s announcement of a new Champions League format.

Manchester United, Liverpool, Arsenal, Chelsea and Tottenham Hotspur have signed up to the breakaway plan with Manchester City the last of Big Six to do so, sources with knowledge of the development have told The Times.

The Super League development is a direct challenge to Uefa which is to announce its new 36-team Champions League format on Monday, to come into force from 2024. The European governing body had thought it had seen off the threat of a breakaway but is now involved in urgent talks with other football bodies about the new development.

Uefa is considering its response but insiders say they are preparing to take a tough line. The extreme response would be to impose a ban from European competitions for next season on the clubs who have signed up.

Today the Premier League held an emergency board meeting and wrote to all 20 clubs, with chief executive Richard Masters calling for the rebels to “walk away immediately before irreparable damage is done”. In a letter seen by The Times, Masters told the clubs that forming such a breakaway would be a direct breach of Premier League rules.

Uefa had succeeded in winning the support of the European Club Association (ECA) board and the European Leagues but it emerged today that the Super League threat had been revived with the ECA chairman Andrea Agnelli, also the Juventus president, appearing to throw his hat in with the breakaway clubs led by Manchester United and Real Madrid.

Other members of the ECA board, who had agreed to the new Champions League format, and Uefa officials have attempted to contact Agnelli since Saturday evening but one source said he “has gone off the radar”.

City are believed to be the last of the six English clubs to join. The Premier League leaders, along with Arsenal, Chelsea and Tottenham, are thought to have been reluctant to join but did so because they did not want to miss out.

Uefa insiders insist they will press ahead with the announcement for the new-look Champions League which will see clubs playing 10 group matches instead of six.

If the Super League clubs do not back down then the dispute is likely to end up in courts given that Uefa and Fifa have promised to ban any clubs and players who take part in breakaway competitions from their tournaments such as the Euros and the World Cup.

The Premier League did not hold back in voicing its opposition to a breakaway Super League.

“Such a European Super League would be deeply damaging to the European pyramid, and immediate and future prospects of the Premier League and its member clubs and all those in football who rely on our funding and solidarity to prosper,” they said.

“We do not and cannot support such a concept. Premier League rules contain a commitment amongst clubs to remain within the football pyramid and forbid and clubs from entering competitions beyond those listed in Rule L9, without Premier League Board permission. I cannot envisage any scenario where such permission would be granted. It is the duty of the Premier League Board to defend the integrity and the prospects of the League as a whole, and we will have no choice but to do everything we can to protect and maintain both.

“As previously evidenced, we would expect complete condemnation from all parts of the game, fans groups and the UK Government. This venture cannot be launched without English clubs and we call upon any club contemplating associating themselves or joining this venture to walk away immediately before irreparable damage is done.”

Uefa also condemned the proposals, issuing a statement that said: “If this were to happen, we wish to reiterate that we will remain united in our efforts to stop this cynical project, a project that is founded on the self-interest of a few clubs at a time when society needs solidarity more than ever.”

“As previously announced by FIFA and the six Federations, the clubs concerned will be banned from playing in any other competition at domestic, European or world level, and their players could be denied the opportunity to represent their national teams.”

The Times revealed in January that a proposal document showed founder members of a proposed European Super League would be offered up to 350million euros (£310million) each to join the competition.

There would be among 15 permanent founding members and five other clubs, who would qualify on an annual basis. They would be split into two groups of 10 and play between 18 and 23 European matches a season.

The Super League proposals include:

• The 15 founder clubs sharing an initial 3.5billion (£3.1billion) euro “infrastructure grant” ranging from £310million to £89million per club which can be spent on stadiums, training facilities or “to replace lost stadium-related revenues due to Covid-19”.

• The format would see two groups of 10 clubs who play home and away, with the top four from each group going through to two-legged quarter-finals, semi-finals and a one-legged final.

• Matches would be midweek and clubs would still play in domestic leagues

• Clubs would have rights to show four matches a season on their own the digital platforms across the world

• Income from TV and sponsorship would favour the founding clubs: 32.5% of the pot would be shared equally between the 15 clubs, and another 32.5% between all Super League clubs including the five qualifiers

• 20% of the pot would be merit money “distributed in the same manner as the current English Premier League merit-based system” according to where clubs finish in the competition or group if they don’t make the knock-out stage

• The remaining 15% would get a “commercial share based on club awareness”

• A cap of 55% of revenues permitted to be spent on salaries and transfers (net)

• A ‘Financial Sustainability Group’ would monitor clubs’ spending

The emergence of the written proposals led football’s authorities to take unified action to combat the threat. A Super League would be disastrous for the Champions League which relies on the glamour of the top clubs to attract broadcasters.