Doc Martin represents one of my guiltier pleasures, in that I watch it in what I think of as my time "off", freed from doing the serious important note-taking shtick or being asked to struggle professionally to fathom the enduring appeal of Downton. The Big Bang Theory, The Wright Stuff, reruns of Jonathan Creek or Endeavour - all are just-for-me equivalents of warm mismatched socks, a hot-water bottle and burnt bubbling cheap cheese on toast. Bliss.

So I dread the day Martin Ellingham - his surname an anagram of showrunner Dominic Minghella, is this interesting? (No, Ed.) - gets all worthy or political or even relevant, and I have to review it seriously. And, the saints be blessed, that still looks roundly unlikely from this sofa. We're still freely invited, 11 years on and at the close of the latest series, to giggle smugly at Cornwall, and what immense fun that is. Those who have been there know that the inhabitants live in perhaps the most glorious corner of God's green earth, and there should be payback, so we're probably entitled to regard the Cornubian batholith as the Land That Education Forgot. Almost everyone be a moron.

Bert Large is a cunning 20-chinned moron. Son Al is a misunderstood moron. Mrs Tishell is a comedy escapee from The Archers, and a moron in italics. Sexy Morwenna is a trainee moron (yet there's hope, and, left to her own devices, she correctly divines that 100% of those waiting for the absent doctor's curt ministrations are slouchy malingerers or alcoholics). King Captain Moron is, of course, PC Joe, who in this final series episode managed to louse up in every way imaginable short of snagging his own pancreas in a bear-trap. Actor John Marquez deserves great credit: not since Father Dougal has there been on our screens a more credible, human, moron.

In the end, after some relatively serious business involving the Doc's kidnapping, serious mainly because one doesn't ever dick about with Gemma Jones possessed of the "nice" end of a shotgun and a righteous wrath, Louisa and Martin were gently reunited. "I think I've been a little bit obsessed with people having to be normal. But they're not, are they?" You said it, girl from Cornwall. Sweeter, more seriously, "I know you weren't going to let me down," which is very much all a girl wants. But... only sometimes. Hence the clever personal tension underwriting the relationship at the heart of this series, and which, apart from the sweet morons and Martin Clunes's deadpan perfections, lends it its entirely fathomable appeal. More, more.

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The Doc's blood phobia is getting worse, as is his consequent insomnia, which is also beginning to disturb his wife Louisa in the marital bed. Maybe it's time he saw that psychologist his Aunty Ruth recommended, particularly when there's an unfortunate and very public incident involving Doc Martin, dopey police officer Penhale and a staple-gun. Penhale (John Marquez) causes widespread panic in Portwenn after jumping to conclusions about an asbestos scare.

But nothing is quite as terrifying as the sight of Martin's poised, chilly mother (played by Claire Bloom) who turns up on his doorstep with some news which, if delivered to any sentient human being other than Martin (Martin Clunes) being would be cause for thoughtfulness and sadness. But not the blithely unempathetic Doc, oh no. Not in a million years.

Some things never change for Doc Martin. The sun always shines. The people of Portwenn always bring him a supply of interesting maladies. And in the series finale he's always seen speeding past tractors in his fancy silver saloon car, averting
a crisis that's inconveniently happening out of town.

So it is tonight, as a long-term supporting character suddenly gets their moment in the spotlight via a slightly creaky personality change. At the end of a faintly disturbing but cosily predictable caper, there's a clever and rather lovely tidying up of frayed ends. You know where we're going, but it's how they get us there.

More importantly, achingly stupid PC Joe Penhale (John Marquez) who's already one of the funniest characters on telly, really ups his game when there's genuine peril about.

The Cornish whimsy continues tonight as Martin (Martin Clunes) and Louisa (Caroline Catz) discover that having a baby can actually cause a surprising number of arguments. They tackle his christening (Martin books it without consulting Louisa), who should return to work and whether the child should go to boarding school one day. Meanwhile PC Penhale (John Marquez) seeks to stop his recently unearthed wife Maggie (Julie Graham) leaving the village and school caretaker Mr Coley (Brian Pettifer) goes completely gaga.

As Louisa and the Doc finally knuckle down this week to naming their poor baby, Julie Graham, who played Martin Clunes's wife in William and Mary, breezes into Portwenn - but this time she's married to PC Joe Penhale (John Marquez).

If your reaction to that is: I didn't know he was even married, well join the club, nor did Joe. But he seems awfully pleased to see Maggie all the same.

It turns out to be another medical puzzler for Doc Martin, whose talent for identifying extremely rare medical conditions rivals even Gregory House's.

It's all the more impressive seeing as the Doc is equipped with just his medical bag.

He usually has to double as a paramedic as well, since the folk of Portwenn have a strange inability to dial 999 - preferring instead to make the poor doctor sprint to each and every emergency.

I do hope that somebody buys him a nice pair of trainers for Christmas.

Another biggish guest star arrives: Julie Graham memorably spent three years as Martin Clunes's screen wife in William and Mary, and here they are again, reunited. Except they're not quite, because in Doc Martin, Graham plays the wife of PC Penhale (John Marquez). That's odd, considering we didn't know he was married. It's even odder that his wife thinks he's only just arrived in Portwenn.

Meanwhile, Cornwall's worst restaurateur Bert Large (Ian McNeice) is deeper in debt than ever, a fisherman keeps fainting, Eileen Atkins desperately deserves more screen time as Aunt Ruth, and Louisa's mother is still causing trouble, above and beyond her annoyingly nomadic accent.

As for the Doc himself, an episode full of the customary, satisfying sight of him being rude to people who fully deserve it has a glimpse of warmth at the end. That it's hard-won makes it all the more affecting - Clunes is brilliant at letting those little flickers shine through.

If you're looking for a bit of escapism then you could do worse than visit the quaint Cornish seaside retreat of Port Wenn in this light - and hugely popular - family drama, now midway through its fifth series. It's easy to see why Martin Clunes's shirty surgeon decided to stay in the idyllic fishing port rather than return to life in London as he nearly did at the end of the last series. The sleepy pace gently washes over you and the magnificent views (in reality those of the village of Port Isaac, which is indeed in Cornwall) transport the viewer to a picture-postcard paradise.

Tonight Clunes's no-nonsense Auntie Ruth (the splendid Eileen Atkins) is on formidable form cheating at chess, berating her chickens, and wanting to "bring back capital punishment for people who use their mobile phones on the train". The programme avoids banality by touching upon some serious medical issues. When PC Penhale's (John Marquez) ex-wife Maggie (guest star Julie Graham) turns up thinking it is April 2008, the Doc quickly spots signs of transient global amnesia and arranges an urgent brain scan.

Terminally dense PC Penhale (John Marquez) provides most of the Cornish clot comedy tonight as rumour of a genetic illness in the family brings on a bout of hypochondria. Meanwhile, with even Doc Edith's (Lia Williams) flirting failing to loosen up our emotionally constipated medic (Martin Clunes), the romantic focus remains on ex-fiancée - but soon-to-be mother of his child - Louisa (Caroline Catz), who has prenatal anxiety.