British no-frills airline EasyJet rejected Thursday a fourth informal takeover proposal from a US private equity firm, but left the door open to possible talks on a higher offer.

Easyjet investors have said they are holding out for at least £600m more from Castlelake, whose bids have been brushed off by the budget airline.

Easyjet has rejected suitor Castlelake for a fourth time but said it could consider a “more attractive proposal”.

Castlelake had submitted a fourth approach for easyJet worth £6.50 a share.