A judge has dismissed all charges against five Extinction Rebellion protesters after a police officer due to give evidence in their case went on holiday.
Deputy District Judge Vincent McDade accused the Crown Prosecution Service (CPS) of “abject failure” over the blunder.
City of London Magistrates' Court heard that a police officer, who was due to be a prosecution witness, was not given enough notice of the trial date and had booked a holiday.
Claudia Fisher, 57, from Brighton, Phoebe Valentine, 23, from Brighton, David Lambert, 60, from Gloucestershire, Senan Clifford, 59, also from Gloucestershire, and John Burrage, 42, from West Wales had been facing trial for aggravated trespass.
They were accused of gluing themselves to the concourse between London City Airport and a DLR station in October.
Before the hearing on Tuesday, a former chief government scientist said he would give evidence in their defence warning that climate change was the “most important issue humanity has ever had to face”.
Professor Sir David King called for “leadership from the very top” and described Brexit as a “distraction”.
“What we are talking about is the most important issue humanity has ever had to face up to,” he added.
“No government, including ours, is doing enough today.
“So what we need is much more action, much more clarity on the action that is needed, and we need it with a public voice.
“And that's what Greta Thunberg and Extinction Rebellion have done. They've put it back on the front pages.”
Sir David, who served as the foreign secretary’s Special Representative for Climate Change, described the actions of the Extinction Rebellion activists as a “brave attempt” to get the “critically important” issue into the spotlight.
Police have been heavily criticised for their response to mass Extinction Rebellion protests centred on London in April and October, where almost 3,000 arrests were made as activists blocked roads and bridges.
Hundreds of demonstrators were detained after the Metropolitan Police issued an order effectively banning Extinction Rebellion protests from the whole of London in April.
A fresh uproar was caused by revelations that counterterror police in the South East had included Extinction Rebellion among other left-wing campaign groups in a document on spotting extremism.
The unit responsible apologised for the “error of judgement” and said it does not classify the global movement as an extremist organisation.
Police said the document would be recalled, but it has now emerged that it had already been circulated to government departments, five police forces and 20 local councils.
The Guardian reported that the guidance was sent to bodies including the Home Office, the Department for Education, Prison Service and NHS England, who all have statutory duties to report extremism under the controversial Prevent programme.
Extinction Rebellion accused police of “trying to silence a peaceful, non-violent movement of people who are trying to make sure the world's children have a future“.
Last week, security minister Brandon Lewis told MPs that Extinction Rebellion was ”in no way considered an extremist group“.
Speaking in the House of Commons, he said: ”We are clear that the right to peaceful protest is a cornerstone of our just society and an indispensable channel of political and social expression.
“The police have recalled the guidance and are reviewing it, and I want to reiterate that Extinction Rebellion is in no way considered an extremist group under the 2015 definition of extremism.”
Additional reporting by PA