Passengers claimed he was even smoking in the toilets.
The commotion got so bad at one point that the captain warned that the plane – full of families and young children – may have to make an unscheduled stop in France.
When the plane touched down in Spain, Brook, 31, and a pal were questioned by cops.
James Robinson, 35, and his girlfriend Megan Christowe, 34, saw first-hand the disturbance Brook and his friend caused on the flight.
James, of Boston, Lincs, said: “Kell and his mate were drunk when they got on the plane and carried on drinking with booze they’d bought in the airport.
“They were loud and Kell’s mate was throwing things around. Everyone was getting pretty annoyed.
“I’ve no idea how they got on the plane. It must be because he’s famous because no normal person would have been allowed.”
At one point the seatbelt sign went on and the captain announced over the tannoy that a passenger was smoking in the toilets.“I wish I’d videoed his behaviour, but you don’t want to pick a fight with a champion boxer”
James Robinson
It is claimed that shortly after the announcement, Kell emerged from the toilet stinking of smoke.
The boozy trip took place in June, just weeks after the Sheffield fi ghter lost his IBF world welterweight title to Errol Spence Jr.
The fight left Brook’s career in question after he suffered a broken eye socket.
Cops confirmed they spoke to Kell and his friend as they came off the plane, but no arrests were made.
James added: “When the plane landed we all had to exit from the rear of the plane as the staff had Kell and his mate at the front waiting for the police. He should have been arrested.
“I snapped a photo of him as we walked past. I wish I’d videoed his behaviour, but you don’t want to pick a fight with a champion boxer.”
An airline spokesman said: “easyJet can confirm that police met a flight from Liverpool to Barcelona on arrival at Barcelona due to two passengers behaving disruptively.
“easyJet’s cabin crew are highly trained to assess and evaluate all situations and to act quickly and appropriately to ensure that the safety of the flight and other passengers is not compromised at any time.
“Whilst such incidents are rare we take them very seriously and do not tolerate abusive or threatening behaviour on board. The safety and wellbeing of passengers and crew is always easyJet’s priority.”
A spokesman for the Civil Guard in Barcelona said: “On June 24 at about 10.50am we received a request that we attend flight arriving from Liverpool. It appeared two difficult passengers were travelling.
“The Civil Guard attended the arrival area for the flight and contacted the personnel on board who informed us that there were two difficult passengers, in a drunken state, bothering passengers during the flight and even smoking on board during the journey.
“The flight captain lodged a complaint with the Civil Guard for breach of air navigation rules by these two passengers, both of whom travelled with British passports.
“The Civil Guard accompanied the passengers to a public area without further incident. Neither of them was arrested.”
A spokesman for Kell Brook declined to make a comment.
