Last year, Stansted brought in 25.9m passengers, a rise of 6.5 per cent over the previous 12 months.
Airport is celebrating a record-breaking year after more passengers than ever flew through the UK's third-largest hub.
"As we are now serving more passengers than at any time in the airport's history, it's imperative that we plan how we can keep pace with demand and invest in developing quality, good value facilities to ensure we do all we can to enhance the passenger experience", O'Toole said.
It was helped by a record month as December saw 925,017 passengers use the terminal.
In December the airport had its busiest ever Christmas period with 1,833,620 passengers jetting off - a 1.5% increase on December 2016.
Adverse weather conditions meant the December figure was down marginally on the same month in 2016.
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Andrew Cowan, CEO of Manchester Airport, said: "It's been another strong year for Manchester Airport as passenger numbers continued to grow and we celebrated the launch of a number of key routes". To carry more than 9.9 million passengers is a huge achievement and testament to the hard work put in by more than 5,000 people across the airport.
"Over the last 12 months we also made considerable improvements to the airport by investing more than £25 million on a number of successful projects including the resurfacing of the runway, increasing aircraft stand capacity and the opening of our new consolidated vehicle rental centre".
Domestic and worldwide traffic was up 4.6 per cent and 8.7 per cent respectively because of strong demand for winter sun destinations, but helicopter traffic was down 11.6 per cent on December 2016.
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2018 promises to see yet more growth, with £1 billion of transformative work ongoing at Terminal 2 and the airport set to increase dual runway operation from the summer.
Carol Benzie, managing director of Aberdeen International Airport, said: "Domestic fixed-wing traffic has driven much of the total passenger increases which has, in part, been due to chartered services being used by offshore workers to reach destinations such as Sumburgh and Wick, to then connect offshore via helicopter".
"This has, as a result, contributed to the decrease in helicopter passengers travelling directly from Aberdeen".
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