The abrupt closure after its overnight missile attack on Israel has left thousands stranded elsewhere.
An Etihad flight from London Heathrow to the UAE was initially diverted to Riyadh, Saudi Arabia.
Wizz Air also several flights to Abu Dhabi diverted.
It was a similar story for Emirates flights to Dubai including London Heathrow, Birmingham and Dublin flights.
More than 80 flights were diverted across 16 airlines.
As well as Iran, the airspace of Israel, Jordan, Iraq and other countries were shut down.
Some flights were turned around while others landed and a third airport within Europe.
“Safety and security are always our highest priorities, and we continuously assess and adjust our operations accordingly,” British Airways said.
Jordan and Iraq have since reopened to flights but Israel and Iran remained closed.
Overflying Iran is a usual route for Europe departures to India and Southeast Asia.