Lord Houchen, elected for a third term as Conservative mayor earlier this month, said the interest was a “massive vote of confidence” in the airport and officials had done “the diligent thing in assessing” the proposals.

“From my point of view I don’t think we should ever be selling our airport, we should be protecting it for the future,” he said.

“So while it shows our 10-year plan is working and private investors can see great value in the airport, it is not for sale and will remain in public ownership.”

Lord Houchen has championed the expansion at the airport, recently announcing a pledge to add new flights to Malaga and Tenerife.

This week, daily flights with Eastern Airways to Aberdeen took off, just weeks after Loganair scrapped its route.

Flights will be increased to twice daily from September, and Lord Houchen said it was “excellent news for the many local workers” who use it to commute to offshore work.