International Airlines Group has revealed it has had a takeover offer, believed to be in the region of £750 million, for Irish flag-carrier Aer Lingus rejected.

Shares in both companies surged as the bid became public, with a potential deal giving IAG-owned British Airways access to valuable landing slots at London Heathrow Airport.

Aer Lingus is the third biggest carrier at the airport.

However, any takeover of Aer Lingus would require the backing of Ryanair and the Irish government, as they both hold stakes in the company.

Ryanair has repeatedly sought to acquire Aer Lingus itself, making any deal fraught with difficulty.

A takeover of Aer Lingus by IAG would also need to satisfy regulators that it would not harm competition on certain routes, or give an undue advantage to IAG in terms of take-off and landing slots at congested airports in the south-east of England.

IAG, which also owns Iberia and the low-cost airline Vueling, added in a statement following the refusal that there could be no certainty that a further proposal would be forthcoming and that another statement would be made “if and when appropriate”.

Aer Lingus operates a fleet of 47 Airbus aircraft and carries more than 10.6 million passengers a year.