There are several tiers of Mitchell and Webb appreciation and awareness. Web savvy Brits will recognise them as the "I'm a Mac and I'm a PC" duo in Apple's all too smug and haughty UK ad campaign (now mercifully over). How dirty that earned money must have felt if part of the contract stipulated that the ads do not appear on TV... It's a very interesting distinction, market and exposure-wise. I'd advertise Macs if I was asked (I'd whore something I deemed worth whoring) but to insist the ads played in one medium... It beggars belief that Harrison Ford and Arnold Schwarzenegger have both done commercials but with contracts that bar the finished whoring from being shown in the US, where of course their reputations would be correctly tarnished. They get to sidestep the humiliation. Our late lamented Bill Hicks would have something to say on that subject but that's my next review...  Have these people not got enough money? Or is the cash siphoned off to charities (in which case, "Bravo!") For his current ubiquity if nothing else, David Mitchell must be making a fair whack. Webb's reasoning after the barbed cries of "Sell out!" was simple. Work a few undemanding days for the same money made on a whole series of Peep Show. It's a no brainer (if money is the sole object of course; I'm not having an opinion on that until someone asks me to flog Macs – which I do for nothing anyway).

Early M&W adopters will know them from the afore mentioned and excellent Peep Show, an innovative and genuinely funny UK Channel 4 take on thirty-somethings mourning their youth now entering its 5th series. Not actually written by M&W (that credit is taken by Jesse Armstrong and Sam Bain), the new series will feature Clive Merrison as Mitchell's father (one of the best Sherlock Holmes incidentally and suddenly made cool in his offspring's eyes because of his association with M&W). Then there's Robert Webb's extraordinary Flashdance routine for Comic Relief and his championing of poet T.S. Eliot in BBC 2's excellent My Life In Verse. Mitchell's solo efforts have him appearing in the rather smart and wry but seemingly ordinary sit-com Jam and Jerusalem in which, as a doctor, he was central to one of the best visual gags I've seen for a while. Faced with a cervical smear procedure on his ex-headmistress, he bolts for the door but already lubed up, gloves on, he can't open it – I can still remember the panic as his hands slip ineffectually at the handle. He had a guest stint in the sublime and silly Bleak Expectations, a Radio 4 series that was so wonderfully daft, you laughed because the cast were having such a riot. Check out ex-Buffy alumnus Anthony Head playing the most evil man in the world, Mr. Gently Benevolent. Mitchell played a priest with a supposedly hideously ugly daughter, Ripely Fecund (oh, it gets much better and much, much worse than that). All three series are a hoot.

But he's perhaps best known to a general UK audience as a ubiquitous, smart and all too welcome guest/and/or presenter on all manner of panel shows on both radio and TV. I happen to think that when it flies, the show Would I Lie To You? hits extemporaneous comic heights and Mitchell is often in danger of revealing the one character trait he seems to try so ironically hard to keep under wraps. The man is angry (as angry as I am) about the horrendous lack of reason in ordinary life, so much so that he often Richter scales the illogic in mirth-quakes well worth witnessing. I apologise for that dreadful word-play. But not sincerely.

So to The Mitchell and Webb Look, Series 4. The Times TV Reviewer (and one time baboon assassin) A.A. Gill, once opined that the quality of the comedy sketch shows in a previous M&W series was so poor that even applying make up to the actors to perform in any of the sketches must have been a dispiriting affair (no pun intended, spirit gum is used in make-up for those not in the biz). I thought that blunderbuss shot a little harsh and had my day brightened when I read that the latest series had him laughing out loud unexpectedly. I'm not certain of the date of the review but I'm petty sure the sketch he must have been watching was the last one of programme one when Mitchell unleashed his angry man as a sociopathic office manager who murdered (with a silenced weapon which was characteristically considerate) any of his employees who made a common verbal faux pas (or as a friend of a friend once remarked, "a foo-pass"). It was fantasy wish fulfilment. I worked with a guy for a number of months and in being specific about something, he used to say "...well, I think pacifically, the lions are the aggressors," or "Pacifically, I'd say he was Dutch." I cracked and in our last week I didn't shoot him with a silenced pistol but reminded him (how can you remind what's obviously not known?) that it was 'specific' not 'pacific'. And it's suddenly struck me that this particular sketch is a reworking of the wonderful In Bruges, where the nasty character played by Ralph Fiennes, lives and dies by his own code. Viewers of both will know what I mean.

No movie (or movie star) these days is allowed to develop an audience or in the parlance, no one has the luxury of failure any more. Well, Mitchell and Webb are proof positive that starting small, working hard, making radio and TV, show after show, series after series, counts. The quality of the 4th season is significantly higher and while the sketches are still something of a grab bag, they are at last consistently amusing, sometimes laugh out loud and more importantly to me, even shocking at times. It's perhaps interesting to note viz-a-viz this 'no one has the luxury of building their craft' anymore that all four series of The Mitchell and Webb Look have had their DVDs distributed by different companies...

Their fourth outing contains no Angel Summoner aside from a recap (a shame as it's one of the highlights of previous series) but it does sometimes lurch into affecting drama that for a sketch show is extraordinary. When the ancient, disfigured and senile dementia inflicted Sherlock Holmes says "I know, John. I do know..." to his Watson, there's a real emotional punch. And it's played that way, a sour, sad affecting thimble of vinegar in an otherwise amusing framework. It caught me unawares. Ending the series on this sketch was almost inevitable. You just couldn't segue into an Angel Summoner after that wonderful display of real acting on both parts.

Of the two discs, the first is simply the six half hours. Highlights of Season 4 include an introduction by the pair answering their critics with a deliciously ironic "We won't make shit anymore as there are more important things in the world..." and then go on to admit this decision was made after they'd shot season 4. When apparently they present themselves as themselves, the effect is both comic and sharp. These are comics who know their audience well (marketing folks at Apple spotted that a few years ago). One of the old favourites is trotted out (I never was a fan of the end of the world quiz show preferring instead the now defunct but gloriously stupid 'Numberwang!') but it's funnier this time around because the stakes are higher. Their 'Arsestore' and 'iBag' cracks at Apple seem a bit mean spirited (depending on how much they made from the commercials that is) but they're both still bloody funny. The conspiracy sketch on the death of Lady Di steers deliciously near the taste knuckle – the laughs are more expressions of shock than comfortable 'Good Life' chuckles. Again on the tasteometer, peaking at 9.9 is the dreamy look in Webb's eyes as he considers there maybe something in the idea of a fast food outlet at Auschwitz with 'Arbeit Macht Fries' in wrought iron above the entrance. "Do you think there's a sketch in it?" "Absolutely not," comes Mitchell's voice of reason.

I do like the duo partly because it seems such an unlikely partnership, like seeing Stephen Fry build a career not with Hugh Laurie but James Cordon. I guess there's some awful self-conscious class recognition going on there in my head but M&W are both Cambridge boys (where they met) – but it's more a personality clash and that clash produces good work and I guess that's the yardstick. This review carries on under the Extras banner a little further down as there's a whole 2nd disc full.

It's a TV sketch show so it looks as good as anything else out there with special lighting and grading giving the right mood when the writing/sketch demands it. The stereo sound is excellent and English subtitles are available though in that awful stencil font that I imagine appeals to no one....

Disc Two is devoted to what is suspiciously titled 'bonus sketches' whose subtext must mean those not deemed good enough to be in the series. We shall see (or rather I shall see in about fifteen seconds...)

Bonus Sketches (51' 33")
Interesting – no laugh track (or no laughing studio audience). And it does make a difference. Some more examples of M&W die-hards (exhausted couple with baby, Hennimore and small office cramming) are trotted out with varying degrees of smile-factor while the footballers as actors – once the punch-line is revealed doesn't stand the test to be brought back a number of times. There's a German Dad's Army which had some potential but settled back on Nazi renders of the famous Dad's Army quotes. There's another shadowy organisation sketch (in the vein of the conspiracy to murder Lady Di in the series) having a crack at keeping aliens a secret. It's a pleasant 50 mins but you're biased from the word go – these didn't make the series so... Conclude what you will.

Outtakes (7' 01")
Ever since Dennis Norden in the 70s brought TV and Movie mistakes into the mainstream, their appeal has not waned in the public eye. I'm a little more jaded being in the business. You can't compare TV/Film-making with any other activity when it comes to cock-ups. We are simply not asked to chortle at a paint job gone badly, a surgeon who's taken off the wrong leg or a talking mime artist. That said, if you like these guys, this is amusing but not pant-wettingly funny.

Extended Outtakes (13' 45")
Uh, exactly as it says – just extensions of the above, a few more smiles, a few more laughs and then a full sketch about a G8 Summit meeting with no blooper in sight. Very odd. Maybe they spent so much money on it (a cast of eight, no less) they felt they'd better include it.

"3m2" of Snow" (1' 38")
A short behind the scenes insert featuring M&W as shot and directed (and playfully disowned) by director Gareth Edwards as it's painfully over-exposed. Filler thunders into mind.

Shooting The Cast (20")
Again, filler comes to mind here – this is simply a re-cut of the violent deaths meted out by master pedant David Mitchell in the best and closing sketch of programme one – uh, with different music. Not sure what the point is, some sort of condemnation of Hollywood excess? Surely not.

Hello and Welcome (2' 42")
M&W do their warm up act essentially warning the layman audience that TV and film work has to be repeated many times to get the coverage (so please laugh); if we screw up, it's OK (so please laugh); and noting that several similar sketches need to be recorded one after the other (budget, logistics, costume, set and lighting considerations) so – you guessed – please laugh despite the fact that the sketches will be spread out over the series. Their ease in front of an audience reflects, one assumes, their real identities. Mitchell is controlled and ironic and Webb is always moving and having fun and both are self-deprecating enough for this to be an entertaining diversion.

A treat for fans and casual viewer alike. If you like your sketch comedy smart, amusing, so near the knuckle it looks like K2, shocking at times and sometimes just rude, then this is a fine addition to your library. Just don't go shooting anyone for mispronouncing 'mispronunciation'...