The Chancellor George Osborne has been in Essex claiming that leaving the EU would be a one way ticket to a poorer Britain.
He spoke alongside political opponents Labour's Ed Balls and Vince Cable from the Liberal Democrats as the Remain campaign staged an event at Stansted Airport.
They warned that Brexit could mean an end to cheap flights and threaten investment such as the new Ryanair training centre which will create 450 jobs.
The Vote Leave campaign pointed out that the Ryanair boss Michael O'Leary said only a few months ago that Brexit would not cause fares to rise.
The Stansted announcement comes after more than 300 business leaders urged Britain to vote to leave the European Union, warning that the country's competitiveness is being undermined by its membership.
In a letter to The Daily Telegraph, they argued that businesses will be "free to grow faster, expand into new markets and create more jobs" if they are unconstrained by EU rules.
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