Some will not have all the tech, which will end the 100ml limit on liquids, ready by 1 June.
The UK’s biggest airports are set to miss the deadline for installing new advanced security scanners that will end the 100ml limit on liquids.
The government told major airports to have the high-tech equipment in place by 1 June 2024.
But Heathrow, Gatwick and Manchester do not expect to have all their scanners ready by then.
Consumer group Which? warned it could cause confusion during the summer holidays.
The group said passengers may expect the hand luggage security rules to have been changed at all UK airports, only to find that is not the case, which could cause delays at security.
When the Department for Transport (DfT) announced the deadline, it said the scanners would both improve security and mean more convenience for people travelling, ending the need for “tiny toiletries”.
The rules requiring liquid items to be taken through security in containers of 100ml or less and put in a clear plastic bag were introduced in 2006 after a plot to bomb a transatlantic flight was foiled.
Airports were originally told to bring in new scanners by 2022, before the deadline was moved to June this year.
They use CT X-ray technology to provide 3D images. That means two litres of liquid can be taken through, inside bags. Laptops can also be left in bags.
They are already used in some other countries including the US.
However, London Gatwick, Heathrow and Manchester are all expected to need extra time to finish installing the new equipment across all their lanes.
That means some lanes will still use the current scanners for this year’s summer holidays, so people will still need to stick to the 100ml liquid limits.
Aviation commentator Sally Gethin outlined some of the reasons for the delay.
“[The scanners] are very heavy. Sometimes the floors in the actual terminal have to be reinforced. The cost is really high for these particular scanners – it’s the latest technology,” she said, also pointing to supply chain issues and airports having to free up staff for training.
Heathrow has already begun introducing the new equipment in three of its four terminals, but cannot guarantee the rollout will be complete by June.
A source pointed out that Heathrow has 146 security lanes, more than any other UK airport, and the installation process had to be carefully managed to avoid hindering the flow of passengers.
The airport is understood to be working with the government on how passengers can be provided with “clear messaging”.
Gatwick said it will have made “significant progress” in both terminals by June but does not expect to finish installation until early next year “after the busy summer peak period has concluded”.
Construction work is under way at Manchester and East Midlands airports to expand terminals to accommodate the new equipment.
A spokesperson for Manchester Airports Group said that while “good progress” was being made, completion of the programme is not expected until 2025.
The BBC understands the DfT may consider allowing airports extensions to complete installations across their whole premises where it deems it “appropriate”.
However, if they miss the deadline without permission, penalties are not being ruled out.
Rory Boland, travel editor at Which?, said: “We’re now going to go into a situation where different [UK] airports have different rules, so at some places you will need to get the liquids out in advance, at others you won’t.”
He said this could cause confusion and hold-ups at security. “You only need a couple of passengers to not be prepared to end up having to wait an extra 10, 20, 30 minutes.
“It is disappointing that we’re in a situation just months ahead of the peak travel period… and major airports aren’t ready.”
Mr Boland said airports’ communication with passengers would be very important.
Travel association Abta advised people planning holidays this summer to double check the rules at each end of their journey.
“It’s important to remember that even if your departure airport in the UK has changed its rules around liquids when you travel later this year, you’ll also need to check the rules that are in place for the airport you’ll be returning from as they may be different,” Abta said.
A DfT spokesperson said: “The UK has some of the most robust aviation security measures in the world and this cutting-edge technology will enhance security and boost the passenger experience.
“We are in regular contact with airports as they move towards [the] June 2024 deadline for upgrading their screening equipment and processes. For security reasons we don’t talk in detail about aviation security measures.”