Brexit and the election of Donald Trump as US President only happened because “moderate and sane” people fell asleep and ignored populist politicians intent on undermining the values of liberal democracy, former Conservative Environment Secretary John Gummer has claimed.

Writing in a blog for the Green Alliance, Lord Deben described the referendum vote to leave the European Union and the imminent arrival of climate science denier Mr Trump in the White House as “two terrible examples of what happens when the obviously sensible is taken for granted”.

He also urged environmentalists to stop behaving as if they were in the minority and explain the reasons why global warming must be addressed in a way that was relevant to the public.

After serving as Environment Secretary under John Major, Lord Deben now chairs the UK’s independent Committee on Climate Change, which was set up to advise the Government.

In the blog, he issued what was essentially a rallying call to defend what many regard as the essence of “British values” – liberal democracy.

“We’ve just had two terrible examples of what happens when the obviously sensible is taken for granted and small groups of well-funded individuals are allowed to seize the agenda and destroy the consensus,” he said.

“Brexit and Trump only happened because the moderate, sane, and considered had fallen asleep on the job, ignoring the constant undermining by press and populist politicians of the standards and values of a liberal democracy.

“The current attack in the UK on the independence of the judiciary and the rule of law shows just how far we have fallen and how we have allowed the few to undermine the accepted standards of all decent people.”

After High Court judges decided that under the law, Theresa May could not use the Royal Prerogative to begin the process of leaving the US by triggering Article 50 and needed parliamentary approval, the judges were declared “Enemies of the People” by some in the right-wing press. This is an infamous phrase used by Stalin and other despots over the ages to demonise their critics.

And Lord Deben expressed concern that Rupert Murdoch, whose business empire includes The Sun and The Times, could gain more power if US media giant Fox, another of his companies, takes over UK broadcaster Sky.

“The timing of the attempt of Rupert Murdoch to extend his already over-mighty influence is a warning to all of us that that battle is by no means over,” Lord Deben said.

Supreme Court Brexit Challenge Show all 13 1 /13 Supreme Court Brexit Challenge Supreme Court Brexit Challenge People wait to enter the public gallery outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Gina Miller, co-founder of investment fund SCM Private arrives at the Supreme court in London on the first day of a four-day hearing Getty Supreme Court Brexit Challenge A man waves the EU flag in front of the Supreme Court Getty Supreme Court Brexit Challenge Satirical artist Kaya Mar poses with two of his paintings in front of the Supreme Court Getty Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin. The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge The eleven Supreme Court Justices will hear the government's appeal, following the High Court's recent decision that only Parliament can trigger Article 50 Getty Supreme Court Brexit Challenge Businesswoman Gina Miller arrives at the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin Getty Supreme Court Brexit Challenge Attorney General Jeremy Wright arrives at the Supreme Court in London EPA Supreme Court Brexit Challenge Protesters outside the Supreme Court in London, where the Government is appealing against a ruling that the Prime Minister must seek MPs' approval to trigger the process of taking Britain out of the European Union PA wire Supreme Court Brexit Challenge A protesters wearing a judge's wigs and robes stands outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge A protester holds up a placard outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters Supreme Court Brexit Challenge Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court Getty Supreme Court Brexit Challenge A man waiting to enter the public gallery waves a European Union flag outside the Supreme Court ahead of the challenge against a court ruling that Theresa May's government requires parliamentary approval to start the process of leaving the European Union, in Parliament Square, central London Reuters

He said it was clear that environmentalists had won the argument over climate change.

But he also added: “It’s certain sure that the world hasn’t grasped the urgency of climate change or of the loss of biodiversity.”

Persuading the general public required a change of tack by campaigners who spent years on the losing side of the argument before the science became effectively certain.

“We environmentalists … have spent too much time trying to make missionary converts,” Lord Deben said.

“Instead, we should be concentrating on concepts and language which makes sense in their own lives. That’s why clean air and cheaper heating are so much more important than climate change and energy efficiency.

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“We must stop being utterly theological and become much more practical. If the Pope can do it so can we.

“Now that our aims are aligned with society’s aims, how do we help business and government achieve them.