A High Court showdown between easyJet founder Sir Stelios Haji-Ioannou and executives from the airline is set to start today.

Haji-Ioannou has accused the carrier of breaching a branding licence agreement established when easyJet floated ten years ago.

The agreement stated that easyJet would keep revenue from its “core” activity of flying airlines, which could not be more than 75% of total revenue.

The court case centres on whether revenue from other sources such as baggage charges or speeding boarding payments should be included in the “core” revenue.

Haji-Ioannou is expected to give evidence on Tuesday or Wednesday, and easyJet chief executive Andy Harrison is also expected to appear in court.

If easyJet loses the case, it could be forced to drop its branding or pay out higher royalties for using the brand.

The court case comes amid wider disagreements between the airline’s management and its founder, who is also its biggest shareholder.

Haji-Ioannou has resigned from the airline’s board in protest at its plans to continue expanding and buying more aircraft during a recession.