The phrase 'national treasure' gets bandied around willy-nilly as much as the word 'legendary' these days. But if anyone deserves such celebratory coinage, then it's the eponymous subject of Alan Bennett's Diaries (BBC Two, Sat 24 Dec, 8pm ★★★★☆). This documentary follows the laureate from Leeds as he prepares to unleash the next instalment of his daily jottings covering 2005-2015, as well as going on the publicity trail for the film adaptation of his 90s memoir and play, The Lady in the Van (which makes its terrestrial premiere straight after on BBC Two, Sat 24 Dec, 9pm). And in proper fish-out-of-water style, he heads for New York to be awarded a Library Lion alongside the likes of Gloria Steinem and Karl Ove Knausgaard, all the while fully in the belief that not a single soul there has much of an idea who he is.

This supremely modest scribe seems barely to have changed down the years: one photo shows a young Bennett in trademark jumper, shirt and tie (only the tweed jacket is missing). Arguably, the only shocking moment over the course of an hour is another picture, taken alongside his partner Rupert, where he's attired in trousers and a casual blue shirt, the top two buttons having been wildly unleashed. Bennett is charming and polite company throughout (when he quotes one critic dubbing him a typical northern 'cunt', it barely registers as possible), reassuringly anti-Tory and pro-EU while taking the threat to the UK's public library system as almost a personal affront.

At one point, Bennett recalls his time in 60s sketch comedy group Beyond the Fringe, alongside Jonathan Miller, Peter Cook and Dudley Moore, as being something of an embarrassment. But no doubt this is more down to Bennett's self-conscious nature and publicity-shy demeanour rather than the work's quality. For Pete'n'Dud fans, hearing that some long-lost material has been resurrected will make this the perfect Christmas. Peter Cook & Dudley Moore: The Missing Sketches (Channel 4, Sat 31 Dec, 8pm ★★★☆☆) reveals a bunch of routines which had been removed from the BBC archive (due to efficient housekeeping rather than anything darkly censorious) before thankfully turning up in some non-Beeb shoeboxes across the world.

As well as being able to view the sketches for ourselves, we witness the immediate reactions of some famous fans. This does give the show a Celebrity Gogglebox ambience, with the mirth expressed veering from the positively giddy Ronnie Wood and Josie Lawrence (though she was justifiably less than keen on the homophobic skit which Cook and Moore filmed in Oz with Barry Humphries) to the more sober reverence and smiling restraint of Richard Ayoade and Will Sharpe (creator of Flowers). With the show's airtime clocking in at just over 45 minutes, it's somewhat irritating to hear Rob Brydon do a Come Dine With Me-esque recap before and immediately after every ad break when surely more commentary or context would have kept things ticking over nicely.

It's hard to know what makes the fans of Mrs Brown's Boys (BBC One, Sun 25 Dec, 10.30pm ★★☆☆☆) tick, but given that they number the many millions, it's sometimes worth trying to fathom it. As the first part of this year's festive double-bill proves, pretend swearing and a lot of smut seem to go a very, very long way. Christmas baubles were probably born to be the butt of a panto-ish genitalia gag, but the excruciating signposting on display here makes it virtually worthless. Even the element which made this show almost watchable (all that corpsing in front of a live studio audience) becomes less pleasing due to its utter inevitability.

Equally as inevitable but somewhat more pleasurable are the plainly dumb antics of Dom Joly as he brings us a Trigger Happy Christmas Special (Channel 4, Sat 24 Dec, 11pm ★★★★☆). Oversize is everything in the Joly comedy world: he pulls a massive plug out of Venice, shouts at a big iPad in the street, and abundantly vapes it up beside less-than-chuffed coffee-shop customers. Never one to dodge putting himself in the firing line, Joly just about escapes without receiving physical assault, even when he takes on the mantle of an irritatingly entitled cyclist pedalling through libraries and offices.

Another man who loves libraries (don't you just love these links?) is former Children's Laureate Michael Rosen whose We're Going on a Bear Hunt (Channel 4, Sat 24 Dec, 7.30pm ★★★☆☆) gets the festive treatment. Channel 4 hit animated paydirt when Raymond Briggs' The Snowman was broadcast around Christmas in 1982 (and, apart from 1984, every year since) and while the station continues to forage for an equally epochal successor, Rosen's tale probably won't be it.

This perfectly serviceable story features some kids escaping the clutches of their mum for the day and pretending that they're attempting to track down a bear. And when they do find one lurking in a cave, rather than ripping their faces straight off, he just ends up being a huge metaphor. The finale's less than profound punch to the gut was never going to match the misery of your best pal melting away into nothing.

But still, it's significantly more enjoyable than Ethel and Ernest (BBC One, Wed 28 Dec, 7.30pm ★★☆☆☆). Another story from the Raymond Briggs canon, this one is all about his own parents and their lives during most of the 20th century as they attempt to adapt to the seismic changes all around them. And, well, they sort-of do, to not much effect. You know something's not gone very right when, after spending over an hour in someone's company, their death leaves you wholly non-plussed. It may be an award-winning tale, but it wreaks, emptily, of self-indulgence.

Other than the annual Tardis-fest, there seems little in the way of rollicking fantasy nonsense this Christmas. Happily, The Last Dragonslayer (Sky 1, Sun 25 Dec, 5.45pm ★★★★☆) takes up the broadsword and cuts through the schedules with a bravura tale wielded from the Jasper Fforde novel series. An excellent cast of Fringe comedy types such as Matt Berry, Eric Lampaert and Nick Mohammed are joined by established names like Richard E Grant, Pauline Collins and Ricky Tomlinson, but the show largely wins or fails on the shoulders of Ellise Chappell (aka her from the next series of Poldark).

Sympathetic without being icky, Chappell plays grown-up orphan Jennifer Strange whose destiny appears to be slaying the last dragon (hence the name). Caught between saving a new family and not betraying her missing mentor, the clock is ticking on everyone's fate.

Another man with experience of semi-mythological flame-breathing beasts is Iain Glen (aka him from Game of Thrones). In Delicious (Sky 1, Fri 30 Dec, 9pm ★★★☆☆) he plays a husky celebrated chef who seems to be taking time out of running a hi-falutin' restaurant to cheat on his second wife (Emilia Fox). Meanwhile, his first betrothed (Dawn French) probably knows more than she's letting on. Whether the remaining episodes will be worth taking a punt on is anyone's guess, but for the moment, the dramatic intrigue is pitched somewhere between Desperate Housewives and Crossroads.