Which? consumer expert Harry Kind said while it was the "beginning of the end" of a system introduced 17 years ago, people should not assume it was a rule change across the board.
"It's really important passengers actually check what the rules are for the airports they're flying from and flying to," he said.
But crucially it should reduce waiting times. Many travellers reported delays of up to an hour at security, and in a recent Which? survey, external 7% said they had missed a flight because of queues, Mr Kind added.
"This change will make a massive difference and reduce the number of people missing flights and losing out on their holidays just because they've got a too big bottle of shampoo."
London City Airport was already the fastest of the UK airports it surveyed for security times, with an average of 12 minutes, he added.
The largest of the UK's airports are rolling out the next generation technology on a gradual basis.
Heathrow trialled 3D scanners in 2017 and said with more security lanes than any other airport installing the new machines was "always going to be complex and take longer".
Gatwick is currently trialling one lane with next generation technology and a spokesperson said passengers should continue to follow all existing rules.
Other airports told the BBC they had no specific date for completion but would be in line with the government deadline of June 2024.
The technology has already been in use by airports in the US, such as Atlanta's Hartsfield-Jackson and Chicago's O'Hare, for a number of years.