The former prime minister warned that “complacency” and “nostalgia” are the routes to a national decline and that the UK’s global influence has relied upon history, fortified by membership of the EU and close ties to the US.
He added: "We are no longer a great power. We will never be so again. In a world of nearly 8 billion people, well under 1% are British. We are a top second-rank power."
Sir John suggested that there was “no consensus” on Brexit and that it had unleashed “a populism that may be difficult to quell.”
He said: "Fiction defeated fact and fostered a belief in a past that never was – whilst boosting enthusiasm for a future that may never be.
"If that mode of politics takes root, it will kill all respect in our system of government".
He added: "In the Brexit Referendum, Britons voted to leave EU. I have never hidden my view, nor have I changed it. To my mind – and I am no starry-eyed European – Brexit is the worst foreign policy decision in my lifetime. Brexit was sold to our electors on false premises."
The comments came in a lecture from the Tory statesman where he also lambasted the government’s “Australia deal” as a “fantasy” and a euphemism for a no-deal Brexit.
Sir John also urged Boris Johnson to hold two Scottish referendums as a way of keeping the United Kingdom together.
The first would be on the independence question and the second would be after negotiations have concluded – with a yes vote required for Scotland to leave the Union.
He said: "The purpose of the second referendum would be that Scottish electors would know what they were voting for, and be able to compare it to what they now have.
"This did not happen with Brexit: had it done so, there may have been no Brexit."
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies