Ryanair chief Michael O’Leary has spoken out strongly against the UK leaving the European Union.

He urged a ‘yes’ vote in the June 23 referendum with Europe’s largest low-fares carrier confirming that it will actively campaign for the UK to stay part of the EU.

Ryanair remains a “committed supporter” of the UK remaining in Europe despite being critical of both UK and EU failure to promote low-fare tourism growth in areas such as Air Passenger Duty (APD) and the continuing indecision over additional runway capacity in the south-east of England.

The airline wants to see EU reform to reduce bureaucracy and become more efficient for the benefit of Europe’s consumers.

But it said the best way to achieve this is for the UK to lead from within the EU and not from outside where like Norway, the UK will still pay, will still obey the rules, but will have no influence over decision making.

“As the UK’s largest airline, Ryanair is absolutely clear that the UK economy and its future growth prospects are stronger as a member of the European Union than they are outside of the EU,” O’Leary said.

Speaking at a press conference in London on Wednesday, O’Leary said he feared British bureaucrats more than those in the EU and warned the UK would lose out on jobs and economic growth if it leaves.

“If the UK exits, Asia and the US will no longer want to invest in the UK and will invest more into other countries like Germany and Ireland,” he said.

O’Leary said MPs leading the Out campaign, including Boris Johnson, were “career politicians” and “passengers when it comes to the economy”.

“We do invest and depend on the strength of the economy,” he said. “Not one of them can answer ‘if we leave Europe what will you do then?’ You will pay and obey like Norway.”

The airline is running adverts in national newspapers on Thursday promoting to stay in Europe and hasn’t ruled out having campaign branding on planes and emailing their customer database with their message.

However, O’Leary said he didn’t think air fares would rise if the UK did leave the EU, despite European policy helping drive down prices.

Instead, he said the British government – in the form of APD and failing to make a decision on expanding airport capacity in London – would cause prices to rise.