Middlesbrough have demanded that Southampton be thrown out of the Championship play-off final if they are found guilty of spying by the Football League (EFL).

Southampton are due to face Hull City at Wembley Stadium next Saturday, with promotion to the Premier League on the line, following a 2-1 aggregate success against Middlesbrough in the semi-finals.

But that tie was overshadowed by suggestions that Tonda Eckert's team gained an unfair advantage by having a member of staff secretly film Middlesbrough's training sessions – which is against EFL rules.

The EFL are investigating the incident, with an independent commission set to meet by Tuesday, at the latest, to decide the outcome.

And in an explosive statement on Friday, Middlesbrough said only a serious sporting sanction would be acceptable if the EFL finds Southampton guilty. 

They said: "The conduct at issue, namely the observation and recording of our training session ahead of a fixture of such significance, goes to the heart of sporting integrity and fair competition. 

"In these circumstances, the only appropriate response is a sporting sanction which would prevent Southampton from participating in the EFL Championship play-off final.

"We remain hopeful that the EFL, as regulator, will pursue such a sanction before the disciplinary commission in order to protect the integrity of the game, safeguard all member clubs, and deter any attempt in the future to obtain an unfair and unlawful advantage in pursuit of promotion to the Premier League."

And the EFL has opened the door to such a sanction by saying that "the outcome of the disciplinary proceedings may yet result in changes" to the play-off final, adding there were contingency plans in place in case the fixture had to be pushed back or altered.