Life's Too Short, BBC2, Thursday To the Manor Reborn, BBC1, Thursday

If you're not getting the joke, perhaps the joke isn't there

Small potatoes: Warwick Davis, Ricky Gervais and Stephen Merchant in Life's Too Short (Ray Burmiston )

Is dwarf-tossing your thing? Does it make you laugh? Because that's how last week's episode of Life's Too Short, the new mockumentary from Ricky Gervais and Stephen Merchant, began.

If you were sitting there, sides splitting, was it because you thought the idea of heaving a dwarf like a tenpin bowl was riotously funny? Or was it because you were able to take a step back, at that very moment, and say, "Now that's some good meta-commentary on the way we treat people of a different height from the majority"? If your response was the former, you're clearly not the most evolved of creatures, but at least you're true to yourself. If your answer was the latter, my suspicion is that you're lying to yourself.

But that is just how fans of this show are justifying its treatment of its chief subject, 3ft 6in Warwick Davis – former Ewok, Hogwarts professor and leprechaun. Davis, they say, came up with the idea for the series, so how could it be demeaning? Yes, he came up with the idea, but he didn't write the scripts. Three weeks in and he's already been stuck in a dog flap, half-submerged in a toilet and encased in a teddy-bear costume. I can only guess he is hoping to prove he can laugh at himself.

The series has attracted substantial opprobrium, some of it aimed in an unfairly personal way at Gervais, who has reacted by misconceiving all critique as being based on envy. But there is a basic problem with the show, which is that even if you don't find its content degrading, it is simply shoddily derivative. Davis plays a character called Warwick Davis who, as in life, runs a talent agency for those of diminutive stature. The departure from reality (one hopes) is that Davis is not only small, but also has small-man syndrome. This results in a character who is just another retread of the David Brent/Extras's Andy Millman formula, complete with glances to camera and absurd delusions of grandeur. We've seen it before – and without feeling quite so degraded.

In this episode, for instance, there is a monologue in which he talks about one dwarf on his agency's roster thus: "Bernard, he's useless ... I told him, 'You want to volunteer for medical experiments, you'd make more money that way.' ... Even if he ends up deformed or deaf and dumb or loses the use of his legs, he'd be no worse than he is now, and he'd have money in the bank."

If that is a speech ridiculing those who think in this way, then the tone is confused by a scene in which we see Davis attend a police station to bail out one of his charges, Paul, who has been arrested for drunk-driving a tricycle down a dual carriageway. Once bailed, Paul makes a getaway on that self-same trike, only to crash and end up on his back, his legs flailing like a beetle's as he tries to right himself. That's physical humour, not a send-up of our response to it; that's laughing at him for his body shape, and that's a shame.

There's pushing the boundaries, then there's Gervais. As evidenced by the "mong" debate, his comedic ethos seems to be about challenging political correctness by being politically incorrect and winking – and that's not good enough. Consider a scene in which Davis turns up at a school to "destroy" a 16-year-old who has posted disparaging comments about him online. Davis accuses the teenager, who at this point is anonymous, of being a gay dwarf fetishist. With the epithets "bum chum" and "bender" ringing in his ears from his classmates, the boy is left in tears. The humour? He's in a wheelchair, making Davis feel embarrassed by his actions. But it's not half cheap to use backward homosexual taunts to get there.

Someone who could never be accused of anything other than perfectly proper behaviour is Penelope Keith. To the Manor Born, for those who don't remember, was an early 1980s sitcom in which Keith played an upper-class woman fallen on hard times. Peter Bowles was the nouveau-riche spiv she fell in with. Quite what happened in any specific episode is lost to the mists of time, but the basic idea was a budding romance. The Manor Reborn sees Keith team up with Flog It!'s Paul Martin to try to restore 500-year-old Avebury Manor in Wiltshire as an immersive National Trust estate.

It's perfectly functional, with Keith offering a running commentary, and it's certainly inoffensive. But it doesn't belong on a Thursday night. It belongs on a Sunday evening when you can safely nod off, reassured that the worst thing that can happen is the seedlings for the Victorian kitchen garden fail to germinate.