That Week On TV: Broadchurch, ITV; Bluestone 42, BBC3

Incidentally, much was said about BBC1's Mayday - a drama by the same production company which was stripped across this week and was also about a youth slain in a small community - clashing with Broadchurch. Indeed, it mercilessly ripped off The Killing's famous shot of the young female victim running, terrified, through woodland. Mayday turned out to be a big red herring, however – it was an enjoyably potty boiler set in a crazy magic village where everyone had a horrific secret, to the point where the guy who'd actually done the murder struggled to stand out.

Broadchurch was the more serious offering. Episode one made clear the obstacles it has to overcome if it's to wash away British crime-drama cliché.

The Killing's extra weapon was that it was complete strangers all talking in foreign, so elements that weren't really new at all felt fresh anyway. Broadchurch groaned with familiar actors putting on fruity, changeable accents that instantly told you the action was set in either Devon or Norfolk. The slight whiff of Doc Martin got stronger when we met Andrew Buchan's popular local plumber: unaware that his son had been killed, he walked down the high street, stopping every six feet to be wished a good morning by a different colourful local. The way the scene was directed made it a surprise when he didn't do a song.

Broadchurch's preamble had nothing to match that unforgettable moment when Sarah Lund realises the woman she is talking to is the mother of the victim. Jodie Whittaker played the mother here, who was at school sports day before she realised – as other kids who hadn't been murdered did sack races in ironic slo-mo – that her boy had gone missing overnight. Afterwards, the news from another driver that the jam they were in had been caused by the police closing the beach caused her to abandon her car and run, already knowing what was on the sand.

Once she saw her son's shoes sticking out of a police tarpaulin and the story began, Broadchurch's heavyweight cast showed its strength. Whittaker's highly physical interpretation of a woman being told for sure that she'd lost her child had raw power, offset by Buchan's quieter shock and useless bravado.

Everyone, though, was in the wake of Olivia Colman, who is the best actress in Britain now. As the policewoman investigating the case who is also a friend of the family, Colman was fraught with horror, resolve and grief. Her crumpling face as her character saw the body immediately made us feel the tragedy of the story, and the urgency to solve the case, in a way that most murder mysteries never do.

The weak link so far is an unexpected one. Nobody doubts David Tennant can act, but he might have been miscast here as DI Alec Hardy, the new sheriff in town who was parachuted in over the Colman character's head despite a questionable record elsewhere ("I was completely exonerated!"). He hasn't yet justified this in terms of police work, or any characteristics outside the troubled-detective norm. Tennant's natural strengths – intense energy, frail vulnerability or both at once – aren't there and haven't been replaced. At the moment he just looks hung over.

Broadchurch is set to go deeper and wider as the murder ripples out. One theme is media scrutiny of the investigation and the victim's family, but this was hilariously undermined in the scenes leading to the arrival of Vicky McClure as a gorgeous/evil national tabloid reporter: Chris Chibnall's script misunderstood the basics of Twitter in two different ways within a minute, then gave us McClure's editor telling her an unsolved child murder wasn't a big story and she should let an agency cover it. Accurately portraying journalism or tech still seems to be an obstacle no British drama can hurdle.

As the first episode ended, all those quirky locals looked shifty as they listened to a TV appeal by DI Hardy. With luck, Broadchurch won't go down the shame-behind-closed-doors route Mayday parodied to death. It needs to stick to the Danish template of hard sleuthing and even harder emotion. Even the great Olivia Colman will require assistance.

Is now, or ever, the right time for a sitcom set among soldiers serving in Afghanistan? Bluestone 42 (Tuesdays BBC3; iPlayer) tested the question with its tales of a British army bomb-disposal unit.

Bluestone 42 is written by Richard Hurst and James Cary, who have both worked on Miranda and are experienced comedy technicians. They kept scenes to a minimum length, filled any gaps with gags, and efficiently established their characters and the central plotline of smooth captain Nick (Oliver Chris) chasing cute female padre Mary (Kelly Adams), who finds him attractive despite herself but constantly rebuffs him.

It was a bit too efficient. This was a fairly conservative workplace sitcom, hung on a talking point that was likely to get commissioning editors and journalists interested. There's no cause to question Hurst and Cary's research, or their interest in the subject matter. What is uncertain is whether the comedy and the subject matter meshed together in the right way.

The soldiers were comedy types: a fussy man, a tomboy, an exceptionally vulgar Scot, an omniscient boss (Tony Gardner) who pops up at inconvenient times. They schemed and joked with each other as the captain and the padre set a will-they-won't-they arc going. With Bluestone 42 unwilling to offer comment on the war itself, the driver for episode one's plot could have been a lost lever-arch file or someone scratching the MD's car.

In fact it was an American colonel (Mike McShane) being fatally shot in the head, the flip treatment of which might well have troubled you if you view Western soldiers in Afghanistan as making a grim but glorious sacrifice. But if you see them as oppressive occupiers, Bluestone 42 had that covered too. The Yank's death was softened in advance by his annoying habit of crowing endlessly about his tour of duty in Fallujah.

Fallujah. Fallujah. The word became a punchline. It's just one of those funny place names, isn't it? Like Penge, or Kidderminster. At least it might be for viewers who are a bit hazy on what happened to the locals there in 2004. Anyway, Nick the raffish captain sorted out all the palaver about the team being fired on by launching an RPG into the Afghans' hut, killing them all and letting us get back to the comedy.

Of course a sitcom in a warzone isn't off-limits. But Bluestone 42 shows that it's... a minefield.

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