On Channel 4's opening night in 1982, Ian McKellen starred in Walter, a drama about a man with learning difficulties who tries to make his way in a cruel world filled with suspicion and derision. In Derek (Channel 4, Wed, 10pm), Ricky Gervais stars as a man with learning difficulties who tries to make his way in a cruel world filled with suspicion and derision. And has Karl Pilkington a best friend.

The contrast couldn't be more stark. Whereas the future knight and Lord of the Rings star simply was Walter, Derek is The Office boy with a greasy haircut, bad knitwear and facial tics. The cynical might view Derek as Gervais making a grovelling apology for 'Mong-gate' when he threw a word around on Twitter in late 2011 which attracted the ire of the Daily Mail (obviously), Susan Boyle and MENCAP. Except the writing of Derek was well under way by then ahead of its pilot episode last spring.

Like the overwhelming majority of modern comics, Gervais' heart is solidly in the right place but the brain has a tendency to force a foot deep into his mouth from time to time. Taking risks and making an inevitable mistake or ten is part of the comedian's job description. Here, though, Gervais has gone almost entirely in the opposite direction. Soundtracked by Einaudi, Derek is overstuffed with manipulative schmaltz, and so sickly-sweet that it requires you to undergo an emergency filling just by switching it on.

Shunning the pratfalls of the pilot, Derek is now a conscience-driven series in which besuited health executives visit the care home where the eponymous 49-year-old works, callously poking around to see where cuts should be made or whose jobs can be exterminated. Oddjob man Dougie (Pilkington) is one obvious candidate for the chop, while the delicate situation is not helped by the inexplicable presence of a sleazy waster Kev (David Earl). He brings a certain David Brentness to proceedings, replacing tugging on his tie with slugging on an endless stream of Special Brew while attempting to force himself onto any female (whether old, obese or other) unfortunate enough to cross his awful path.

Gervais' triumphs here are to show that the previously irritating Pilkington is actually half-a-decent actor and to write a beautiful lead role for Kerry Godliman as the stoic care home leader. Where it falls spectacularly down is through some rather lazy button-pushing (especially with the endless photo-montages of aged residents in their youthful pomp) and in Gervais' massively distracting central performance which hinders rather than helps the series. And will he ever give the mockumentary genre a break?

Santa delivers a double header of festive banter tonight. For Alan Carr's final show, Gordon Ramsay discusses his Christmas Day cook-along, Ian McKellen talks about The Hobbit, and music comes from Kylie. Graham Norton's sofa looks more A-list, with Hollywood actor Dustin Hoffman alongside Billy Connolly, one of the stars of Hoffman's directorial debut, Quartet. Doctor Who's Matt Smith and Jennifer Saunders round off the foursome.

The last in the series proved as unmoving and unfunny as the rest, as the pair reviewed The Angel at Hetton. Lines like, "behind every vaguely amusing one-liner is a cry for help," are clearly supposed to be part of a post-post-modern joint self-portrait, but The Trip was always too self-conscious to really make a point.

Coogan's expression of biting misery as Brydon shouted poetry at him in the manner of Ian McKellen by the ruins of Bolton Abbey was a standout moment. But superbly funny as it was, the scene was an anomaly in this programme, which was as unamusing as the preceding episodes.

Broadcast relatively late on Monday evenings, the show has been a little too subtle to keep the viewer's urge to fall asleep at bay and a little too lacking in punchlines to warrant fighting that urge.

With their endless flood of impressions, cynicism and one-upmanship, the pair were trying to convey to us what a nightmare it is to be in the company of show-off comedians, with all their demons of self-doubt.

It worked; it was indeed something of a nightmare to be in this pair's company for half an hour each week. The nightmare of an uncomical comedy cannot be understated.

Finally, we were subjected to a plodding, maudlin finish as Brydon returned home to the eager embrace of his wife and child, while Coogan entered his minimalist apartment alone and had a drink. Whatever could they be trying to tell us?

The end of the episode - and the end, therefore, of the series - left nothing but disappointment in its wake. Like the morning after a particularly drunken evening, the only reason you knew something had happened was because time had passed and while it wasn't clear exactly what had been going on, it definitely wasn't as good as you were hoping it would be.

Sir Ian McKellen to star in zombie costume drama

Sir Ian McKellen, who has mastered a dazzling panoply of Shakespearean roles on stage and is considered one of the most serious screen talents of his generation, is to star in a low-budget zombie costume drama set in the rural backwaters of Britain.

Sir Ian, who has taken on mischievous pantomime roles in the past - he played Widow Twankey in a production of Aladdin at the Old Vic in 2004 - has been cast as a member of the undead in E'gad Zombies!, a black comedy set in the 18th century which is causing a stir at the Cannes Film Festival.

With his hangdog expression and fruity Edinburgh burr Alastair Sim created numerous whimsical characters during a career on stage and screen that spanned more than 40 years - perhaps none more memorable than the creepily convincing Miss Fritton, headmistress in the St Trinian's films. This 1997 profile celebrates his achievements and speaks to his widow Naomi Plaskitt (Sim died in 1976), as well as hearing from friends, co-stars and admirers, including George Cole, Stephen Fry, Ian McKellen, Patricia Routledge and Nigel Hawthorne.