Passengers at Manchester Airport face the longest queues at security of all the UK's largest airports, according to a survey by Which?
The consumer group found the average wait time at Terminal One was about 17 minutes compared to eight-and-a-half minutes at Heathrow's Terminal 5.
When asked how long they waited at security, one holidaymaker said they queued for 90 minutes at Manchester.
A spokesperson for Manchester Airport said the survey was "flawed".
Almost 4,500 passengers were asked to provide an estimation of how long they waited at security on their most recent visit to UK airports.
According to Which?, the longest waits were experienced at Manchester Airport terminals, T1 (17 mins), T2 and T3 (both 15.5 mins).
The next worst performing large UK airport was Stansted (13.7 mins) with the shortest waits at Gatwick South and Heathrow T5 (8.6 mins).
The study also ranked Belfast International as the worst small airport for security queues, with a typical wait time of 22 minutes.
Which? also said Manchester Airport appears to have downgraded security waiting time targets from getting 95% of passengers through in less than eight minutes in 2017, to 92% through within 15 minutes in 2019.
A spokesperson from Manchester Airport criticised the survey, claiming the Which? figures were based on a "limited sample size" and "were not time-specific".
In the past 12 months, 97.3% of passengers queued for 15 minutes or less, he added.
"We monitor actual waiting time performance in security on a daily basis. For most of the last year, the average waiting time at Manchester Airport was around two minutes."
Which responded by saying: "We use responses given by real passengers to provide an average estimated queue time for each airport."
Rory Boland, editor of Which? Travel magazine, said: "Never-ending queues through security are a pain at the best of times, but if you are left waiting for hours on end you could find your flight has left without you."
"Airlines will rarely delay a flight due to long queues at security so it's important to arrive at the airport in plenty of time, especially if you are flying from Manchester or Belfast."