Ross Kemp loves danger the way the rest of us love suspending our disbelief in front of a long-running BBC soap. So, it’s no surprise that after pursuing gangs, pirates, Isis fighters, British troops in Afghanistan, illegal loggers in the Amazon, drug dealers, Tiffany and a whole lot of publicity, the actor-turned-investigative-journalist turns his attention to the deadliest migrant route in the world. The 1,000 miles of Libyan desert, a journey more dangerous than the sea, followed by the treacherous Mediterranean crossing from Tripoli to Italy in rubber boats unfit for purpose. Three thousand people make this journey every week. Twelve die each day.

In Ross Kemp: Libya’s Migrant Hell (Sky1, 9pm), which should really be called Refugees’ Libyan Hell, he tracks the route with his usual brawn studded with the occasional fleck of emotion. This is not nuanced film-making, but somehow that feels right for an issue so huge, horrifying and urgent; a bit of plain-spoken directness feels welcome. Beginning in the Sahara, where threats include smugglers, Isis training camps, armed militias and kidnappers, Kemp intercepts a truck rammed with 22 people. “We are running for our lives,” one man explains. Later, he joins 30 men and women on a 350-mile desert stretch to the next handover point: a seven-hour journey travelling 70mph in 45C heat. Instantly sweating like a pig in his headscarf, Kemp declares: “I don’t think I could do it, that’s for sure.”

Yet do it he does. Why? “It’s only right, if we want to understand what these people go through, to experience a bit of it myself.” Perhaps Kemp cannot see that a white male western film-maker joining some of the most traumatised people on the planet for a mini leg of their journey before returning to his armoured vehicle probably still won’t be able to understand what they are going through.

What Kemp can do is show us the horrors he finds; his access – what with being a white male western filmmaker who looks like Grant Mitchell – is amazing. He meets women held in a house against their will and forced to work in what is clearly the sex trade. He enters one of Tripoli’s three recognised detention centres, where 490 male refugees are locked up indefinitely, beaten, starved and abandoned by every person and government in the world. He interviews a smuggler who has transported 2,000 people into Europe along a coast where smuggling now accounts for half of the local economy. And he spends a night at sea with the Libyan coastguard, getting shot at in the process (this being a Kemp documentary) and rescuing 750 people in just nine hours. Rescue, though, is the wrong word. We have seen the detention centres to which they will be taken.

In the most distressing scene, Kemp visits one such centre for women and meets a woman and two small boys rescued from the Mediterranean the previous night. Out of 120 people, only 18 survived: the boys’ mother was not one of them. “Do these boys understand what happened to their mother yet?” Kemp asks, as they look on with blank expressions. “No idea,” the woman replies before bursting into tears. Another woman, unable to leave her bed, tells Kemp about the baby she recently birthed “inside the toilet”, who died a week later. “Now I’m dying also,” she wails. “I’m dying. I’m dying. I’m dying.”

Kemp’s style may be about as subtle as a sledgehammer, but when he says, with tears in his eyes, that “I don’t care who you are or where you come from … as human beings we have a duty to try and stop this suffering,” it’s a deeply powerful plea. So yes, we now live in a world where Ross Kemp is a rare public voice of compassion and reason in the immigration debate.

Inside No 9 (BBC2, 10pm) is back for a full third series after a Christmas special and is as nasty, brutish and short as ever. It’s a masterclass in how to cram a plot, fully fleshed out (and flesh-crawling) character and a dozen twists into 30 minutes. This episode has a simple premise: four men argue over who’s going to pay the bill in a restaurant. Three are northern (two played by creators Reece Shearsmith and Steve Pemberton), the fourth is a brash, lecherous Londoner (Philip Glenister) willing to risk the safety of his sleeping children in order to prove he has an Amex gold card; all are heinous. Cue lots of northern/southern caricature skewering, and a particularly disgusting lie about a brain tumour. Naturally, it all comes to blows, or rather a nail-biting game involving a knife and five fingers. As Archie (Shearsmith) points out: “There’s always a bill. Somebody has to pay.”