Gwen Stefani and Robbie Williamsare being lined-up as guest judges on Dannii Minogue's decision to [uuid=0b8d2265-d27c-481f-9a96-fd3341e5a1f5]Alicia Keys is also set to make an appearance on the show's judging panel - along with rock veteran Rod Stewart, as [uuid=151216d2-bdc4-439e-a23f-64313c51a28f]Katy Perry, Rihannaand Nicole Scherzinger have all turned down the opportunity to be guest judges on the show, the filming of which begins on Wednesday in Liverpool.
A source told the paper: "At this rate the fourth judge may not be signed until much later in the series. Dannii turning them down was a massive blow because as far as ITV1 and The X Factor were concerned it was a done deal.
"The back-up plan is to have a host of guest performers take part in the regional auditions and possible Boot Camp before revealing a permanent name at the Judges' Houses in August. Everyone involved knows how important the judges are to the success of the show.
"Numerous high-profile singers have come forward wanting the job. But bosses fear they aren't big enough names to wow viewers. So it's now panic stations to make sure they can sign up a big enough name in time."
There are various reports of candidates for a permanent seat on the judging panel, with former Geri Halliwelland Mel Band The Saturdays singers Frankie Sandford and Rochelle Wiseman all claimed to be in the frame.