THERE are only four possible answers to a direct question.

They are: “Yes”, “no”, “don’t know” and “won’t say”.

That was the premise on which the politician-turned-interviewer Brian Walden used to conduct his interviews.

For younger readers, I should explain that Walden was best known for presenting Weekend World, a Sunday lunchtime show in which he could interview a single politician for anything up to 50 minutes.

Walden said it was his first editor, David Cox, who pointed out those four possible answers, and insisted that an interview should be meticulously planned by the journalist. Walden would have to memorise an elaborate flow chart ahead of each interview, with follow-up questions prepared for each use of “yes”, “no”, “don’t know” or “won’t say”.

I often think of Walden’s four answers when I hear front-rank politicians on the airwaves.

Given repeated opportunities to say “yes” or “no”, many of them will stall and flannel in a fashion that can only mean “won’t say”.

Politicians, and other people in the public eye, have been coached to avoid gaffes at all costs They’ve learned to keep repeating their rehearsed message, whatever the question.

Of course, nobody outside the political and corporate world talks in this fashion. If your partner asks whether you’re sure you’ve put the rubbish out, you’re unlikely to say: “What I’m sure of is that the rubbish has been put out every other Thursday for the past 12 months and we’re putting out more rubbish than ever before.”

Not everyone in public life talks like this, but plain speaking tends to decline as people’s careers advance. It’s quite easy to find backbench MPs or local councillors who will call a spade a spade. But those on the front benches are much more likely to call it a manually-powered bladed cultivation instrument and insist the real issue is how we’re getting Britain digging again.

In recent times, politicians have seized on a new way of avoiding a direct answer.

It’s the phrase: “I don’t recognise that.”

It seems to be used by senior people in almost all parties. The chancellor, Philip Hammond, was reported, earlier this year, to have had some angry, sweary exchanges with some of the prime minister’s advisers.

“This is tittle-tattle. I don’t recognise any of this stuff,” he said.

It’s a handy phrase, because it sounds a bit like a denial, without actually being one. Basically, it means “won’t say”.

This sort of thing has made the big 8.10am interview on Radio 4’s Today programme almost impossible to listen to, for me. It’s a slot where it seems politicians only aim to survive 10 minutes without committing a blunder, or even saying anything definitive at all.

But there’s a vicious circle at work. When interviewees refuse to speak candidly, interviewers become keener to catch them out, and the interviewees become more cautious still. That’s why, on Today, the big interview is often followed by the BBC’s political editor telling us what that interview really signifies.

I fear that such lack of candour is not just annoying but dangerous.

When leading political figures don’t speak plainly, the vacuum is often filled by people at the fringes. These are people who get on air precisely because they don’t pussyfoot. Their followers will tell you: “I like him because he says the things other people are afraid to say.”

Perhaps the logical end result is that you end up with a US president who has said global warming is a hoax, vaccinations cause autism, President Obama wasn’t born in the US, and any news coverage which falls short of adulation is “fake news”. All those are forthright opinions. They just happen to be poppycock.

If some moderate people don’t start giving straight yes/no answers, they will run the risk of making extremists stronger.

But I don’t suppose they’d recognise that.