Fifteen of the 24 Championship clubs have threatened to break away if the English Football League refuses to rip up its proposed domestic broadcast rights deal with Sky Sports, Press Association Sport reports.

The threat was made in letters sent to the EFL's interim chair Debbie Jevans last week, after 16 Championship clubs met before crisis talks with the league last Tuesday to discuss the 14-month dispute over the Sky deal.

At that pre-meeting, which the EFL was not invited to, a nine-question survey was distributed which included questions about how willing clubs would be to leave the EFL if the league ignored their opposition to Sky's offer of £600million over five years from the start of next season.

That agreement was first announced in September 2017 and was approved by Leagues One and Two. Championships clubs, however, told the EFL Board to try again as many of them believed it was nowhere near enough money.

Derby owner Mel Morris was the most vocal critic of the deal initially but it is Leeds owner Andrea Radrizzani who has made the most explicit threats about a breakaway league.

Speaking in London last month, the Italian businessman criticised the EFL for its "small money" broadcast deals, which it then splits with 72 clubs, and added: "Maybe (clubs) need to consider another way to create a Premier League 2 or something else, that can be sustainable, even for who is not promoted."

When EFL chief executive Shaun Harvey announced the deal with Sky in September 2017, he described the offer as the "very best deal, with the best partner" at "an incredibly challenging" time for domestic sports rights.

At £120million a season, it is a 36 per cent increase on the current £88.3million a season, but it allows Sky to broadcast 150 EFL games a season, up from 127 this campaign, and the right to stream midweek games.

Harvey's claim that is a good price was bolstered when the Premier League saw the value of its domestic rights fail to grow when they went to market earlier this year but the likes of Aston Villa, Derby and Leeds can point to the large audiences they attract and the fact the EFL deal is worth about seven per cent of the Premier League's.

Press Association Sport report the threat to break away from the EFL was not explicitly made in the documents sent to Jevans but "drastic action" was promised if the league signs the deal, which has a deadline of next Monday, having already been extended.

It is also not clear if all 15 of the clubs are as ready to jump ship as the ringleaders are, with some just wanting a bigger say in how the league sells its broadcast and commercial rights.

Sky Sports declined to comment on the matter but no other party is understood to have come forward with a better offer.

In a statement, an EFL spokesman said: "The EFL sells its domestic broadcasting rights on behalf of its 72 members across the three EFL divisions.

"Recently, a number of Championship clubs have raised some questions in regard to the value being generated by the sale of those rights. These views have been shared with the EFL Board who are currently considering the matter."