ITV blocked a guest appearance by sport presenter Des Lynam on news quiz Have I Got News For You, the channel has said.
Des Lynam's contract with ITV runs out next year
Lynam, one of ITV's biggest stars, is tied to an exclusive contract and the network does not want him to appear on rival channels, a spokeswoman said.
"Unfortunately for Des, he does have to come and ask our permission," she said, adding it was not an unusual decision.
Lynam, who is to retire from sports TV next year, was asked to be guest host for one episode of the BBC programme.
The ITV spokeswoman said: "In the same way that the BBC doesn't let people from EastEnders go on the Frank Skinner show, it's the same with any exclusive stars. The BBC do it all the time.
"We have very, very few exclusive stars and Des is one of them, and there was lots of other stuff going on at the time.
"On this occasion, it was decided that he wasn't going to do it."
Have I Got News For You has been using guest presenters for more than a year since former host Angus Deayton was sacked amid allegations about his private life.
A BBC spokeswoman said: "We did approach [Lynam] and he wanted to do it but then he wasn't able to."
Lynam told the Daily Mirror newspaper: "I was very keen to do it but was told I couldn't."
Lynam, who worked for the BBC for 30 years - fronting shows like Match of the Day - will leave ITV after the Euro 2004 football championships.
The 60-year-old presenter joined the network in 1999 when it won the rights to screen Premiership football highlights.