YAWN? Big, open-mouthed, Grand Canyon-sized yawn? Well, that would be the expected reaction at being subjected to yet another documentary about the death in 1997 of the world’s most famous woman.

Investigating Diana (C4, Sunday) suggested that it would simply offer another opportunity for legal forces to say “We did our very best, and no stone was left unturned in our investigations, Guv. Honest.”

We expected, and in this case our expectations were accurate, that the flip side to this record featured a nod to the conspiracy theorists, such as Mohammed Al-Fayed, father of the princess’s most recent lover, who claimed vociferously that the couple had been murdered by ‘Dark Forces’.

And so, this first in the four-parter played out.

The documentary makers ticked all the expected boxes in carrying out interviews with the French police, who spoke incessantly about the importance of the concept of truth, as if to suggest the alternative was unimportant.

Yet, what struck me about this documentary was that still the same old unanswered questions about the car crash in the Parisian tunnel have never been explained.

What of the witnesses who saw the white Fiat bump the the princess’s Mercedes? What of the flashing light that could have blinded the driver? What of the Fiat driver who took his own life? What of the friends of driver Henri Paul who said he was a stand-up guy and would never have drunk to the point of being four times over the limit? Were the witnesses and friends making it all up?

And why did the British police go to such great lengths to question the veracity of whether Diana and Dodi were about to be engaged, to the point of investigating the jewellery factory where the ring had been crafted?

Yet, this raised questions about the intent of the documentary makers.

The police, here and in France, were not grilled about where they threw their weight (or lack of it). Did raising questions about how close the couple were mean there was no motive for having them killed? But then again, they didn’t have to be grilled. The French police looked to be lacking when they continually trotted out the line “Where is the evidence for the conspiracy theories?” Where was the evidence to suggest the witnesses had reason to lie?

What did we learn from Episode One? The French police ‘combed’ the crash site so meticulously they found one of Diana’s pearls. Yet, the British police said later the site hadn’t been swept carefully enough.

Those who believe there was a conspiracy will have that thought enhanced.

Where this documentary was certainly successful was in offering up a reminder of several thoughts; the popularity of the People’s Princess was almost immeasurable.

But she had in fact called upon legal advice, predicting her own death in a car crash, saying she expected to be murdered. Such remarkable – and unexplained – prescience.

What is also remarkable is the Michael Portillo success story, The Pyrenees with Michael Portillo, (C5 Tuesday). The former Conservative Cabinet minister-turned travel presenter has long managed to pull us in with his plucky enthusiasm for the world around him; my, he’s such an avid train supporter he could (almost) become Mick Lynch’s poster boy.

What was striking about this trip to the mountains of the Basque region was that on the edge of his 70th birthday Portillo is still prepared to forego personal comfort – and perhaps concerns for personal health – to look smashing.

There he was in his mustard cashmere and bright-coloured slacks battling his way through blizzards, pitting his knee cartilage against the roughest terrain.

Yet, while Portillo’s clothes are never understated his natural manner is.

And along the way the travelogue melded with his personal story. His father was a left-wing politician who fled Franco’s Spain, and on the long walk to the UK, met the Scots woman who would become his wife. It revealed real colour in his life, almost as colourful as his range of coats and jackets.

Another tale of stoicism and survival was revealed in The Accused, National Treasures on Trial (C4, Wednesday) which recalled how the likes of Sir Cliff Richard, DJ Paul Gambaccini and former Pop Idol Judge Neil Fox had their lives altered immeasurably by police investigations.

As part of Operation Yewtree which probed sex scandals in the UK (the Met clearly determined not to allow another Saville to escape justice) we learned of a police force with all the investigating nuance and subtlety of an episode of Scooby Doo episode.

Yet, the Met, accused by several media outlets for undermining the presumption of innocence was given space to argue that while their tactics were not perfect, convictions were obtained in the form of Stuart Hall, Rolf Harris, PR guru Max Clifford, and weatherman Fred Talbot.