Qatar Airways now owns 15.01% of IAG, which is the parent company for British Airways, Aer Lingus, Iberia and Vueling. Qatar raised its stake from 9.99% to just under 12% on April 27 after purchasing the original shareholding in January 2015.

In a Stock Exchange statement, Qatar said it “may consider increasing its stake further over time within the allowable limits”, taken as meaning that it could purchase the full 49% allowable under rules that limit ownership of IAG by a non-European Union entity.

The latest deal comes only days after British Airways announced it would make its Heathrow-Doha flights non-stop, meaning they are a more viable option for connections with Qatar Airways, which is a oneworld alliance partner.

Qatar Airways chief executive Akbar Al Baker said: "We have been very happy with our investment in IAG, from a financial, commercial and strategic perspective. The relationship formed has helped to deliver on our westbound strategy. Furthermore, IAG’s proven management and strategic direction have been the basis on which we will continue to forge a long-term relationship.”