Image copyright AFP Image caption Jess Phillips has said Labour must "tell the truth" to win back voters

Someone wise, or at least successful, once said: "The secret of success is sincerity. Once you can fake that, you've got it made."

That immortal advice has been variously attributed to the great Groucho Marx, to the 1940s US comedian George Burns, to the French diplomat and writer Jean Giraudoux but never - ever - to the Labour MP and leadership contender Jess Phillips.

Speaking to me on my BBC 5 live programme Pienaar's Politics, the Birmingham Yardley MP seemed wholly unscripted.

She seemed wary of upsetting party members, but still managed, I'm guessing, to upset and perhaps infuriate thousands of them.

In an age of cynicism and spin, Jess Phillips was authentic and frank in a way which illustrated perfectly why she seems to have little or no chance of becoming Labour's next leader.

Jess Phillips answered my first question, "Should a party leader tell members what they don't want to hear?", with a rapid and sincere "absolutely".

For a moment, conventional political judgement seemed to kick in. She became a little hesitant and evasive about which policies she'd like to erase from Labour's failed election manifesto.

A moment later, she was in full flow. The promise of free broadband was "rubbish," mass renationalisation of utilities, including water, should not be a priority "while there are still homeless people on the street and still, you know, young lads getting murdered on most streets in most cities."

In other words, she was saying, forget about these totemic ideologically driven pledges. There are many, much more important things to do.

Media playback is unsupported on your device Media caption Four candidates remain in the race for the Labour leadership

It's safe to say this is the sort of thinking which wholly alienates the pure-blood socialists who flocked to Jeremy Corbyn's banner.

It is also the very last thing you can expect to hear from Sir Keir Starmer, the frontrunner who's considered not just a Labour centrist, but one who'd be completely at home in any past Blair or Brown cabinet.

Sir Keir is most unlikely to describe himself in that way at any point in the contest. He also has a very good chance of being elected. The two things are related.

Rebecca Long-Bailey may well endorse Labour's last manifesto, and she could win too, which says a lot about the party membership, and helps to explains Sir Keir's caution.

Too much honesty?

We like authenticity and lack of guile in our politicians - or say we do. Except when they're honestly saying things we don't want to hear, or seem artless.

Honesty may have become a dwindling asset in politics. In any event, too much of it can be a liability.

By contrast, International Development Secretary Alok Sharma, who also joined me on air, managed to speak at considerable length about his sensitive and vitally important role without saying anything very controversial at all.

As the UK carves out a new role in the world, Boris Johnson has spoken about the need for "smarter" use of overseas aid.

Priti Patel, the former international development secretary - now promoted to the Home Office - said the UK needed to target aid spending in a way which better served the UK's economic needs and global influence.

So did this mean less money for purely humanitarian help? Was this a significant change of policy? Not at all, according to the minister.

"We are…I mean, we just want to be clear that there's not been a change," he told me.

"We have been doing this. Economic development has been something that the department has been doing for a long time."

I was left none the wiser. Which, I couldn't help feeling, was the point.

Image copyright AFP Image caption Alok Sharma has been international development secretary since July last year

Mr Sharma joined me to talk about the Africa summit which the UK is hosting, and we did.

He also put on a convincing display of why he is one of the few ministers sufficiently trusted by Downing Street to pop up to be interviewed in radio and television studios on a Sunday.

Of course, the prime minister sometimes manages things in his own unique way. He says what he likes, or what best serves his purpose at any given moment.

If a statement or pledge turns out to be problematic or wrong, Mr Johnson seems perfectly comfortable saying something else.

Take the example of the PM's talk of making Big Ben bong to mark the UK's exit from the EU, or past promises on the conduct of Brexit. Can anyone say today a prime ministerial pronouncement should always be considered wholly trustworthy?

Can anyone say it's a question which has done the PM or his government any political harm?

Judging by the latest opinion poll which gives the Conservatives a whopping 17-point lead, the answer is surely no. Well, not yet, anyway.