The dire financial state of the Football League Championship has been revealed by the Guardian’s analysis of the 24 clubs’ most recent accounts, which shows they owed a combined debt of almost £1bn.

The division’s severe difficulties are caused principally by the financial chasm between the Championship and the Premier League, which means promotion, which will be claimed by either Derby County or Queens Park Rangers in Saturday’sWembley play-off final, is worth at least £120m.

Shaun Harvey, the Football League’s chief executive, pointed out this means that the winner will receive the same from one season in the Premier League as “from playing in the Championship for the next 30 years”.

Harvey said the losses, made by 20 of the 24 clubs, £349m overall, and the reliance on owners’ funding – mostly with loans charging interest – prompted the introduction of financial fair play rules which will be enforced for the first time this summer.

In the 2012-13 season, the year of the most recently published accounts, when Hull City, Cardiff City and Crystal Palace were promoted, the 24 Championship clubs spent more collectively on wages, £460m, than their entire income, £430m. They were a combined £947m in debt, mostly to owners supplying interest-bearing loans to pay wages of players they hope will claim the lucrative prize of Premier League promotion.

The financial gap between the top two divisions is the widest since the Football League’s First Division clubs broke away to form the Premier League in 1992 and stopped sharing their television money with the other three divisions.

The 20 Premier League clubs are now sharing £5.5bn from broadcasters between 2013 and 2016, meaning that even the bottom-placed club will be paid at least £60m from television. Parachute payments for the three clubs relegated to the Championship, intended to soften the financial landing, have been massively increased, to £59m over four years – hence the minimum £120m promotion jackpot figure. By contrast, the Football League’s current TV deal is worth £195m over three years from 2012-13, just 3.5% of the Premier League’s. Championship clubs receive 64% of the money, which means they are paid £1.7m each, a dominance itself resented by League One and Two clubs.

That is topped up to a total of £4m with £2.3m from the Premier League in “solidarity” payments, a recognition by the 20 top clubs of the vast financial gap the breakaway opened up.

Harvey said that while the £120m bonanza of promotion is “a fantastic opportunity” for the promoted clubs, the hunger to achieve it has caused clubs to increase spending on players’ wages, and financial pressure on the Championship.

“Increasingly club owners are having to invest more money just to avoid relegation and that cannot continue indefinitely as owners will run out of money and football could run out of owners,” Harvey said.

At his former club, Leeds United, the owner that Harvey worked for, Ken Bates, sold the club with cash-flow problems to the Bahrain-based bank Gulf Finance House. They loaned it £11m, according to the accounts, before in turn selling to the Italian-US businessman Massimo Cellino.

The league is awaiting the written ruling of an Italian court which has found Cellino guilty of tax evasion, to see if he did so dishonestly, in which case Cellino will be barred from being an owner or director, plunging Leeds into crisis again.

Harvey explained that the financial fair play rules are aimed at staunching the huge losses made by Championship clubs. The rules allow clubs to lose £3m this year, plus a further £5m if paid in by an owner. If that is exceeded, clubs will face a transfer embargo, or a fine if they are promoted.

QPR are expected to have made a huge loss this season above the permitted £8m total, so will face a substantial fine if they win Saturday’s play-off final.