Peep Show has come to occupy a curious place in the comedy landscape. Cited by many as being the funniest sitcom of its age, it performs so poorly in the ratings it probably survives only through Channel 4′s lack of other critically acclaimed sitcoms.

Now into its fourth series, David Mitchell and Robert Webb are being seen as the next generation of comedy greats, despite both the ratings, and the fact their other work (sketch show That Mitchell and Webb Look, for example), rarely match Peep Show‘s standards.

Having loved every minute of the first three series, I’m not quite sure what to make of the current run. Although it has contained some uproariously funny moments, there seems to be something slightly different – something I couldn’t quite put my finger on until now.

One neat idea is the inversion of previous theme detailing Mark’s obsession with workmate Sophie. Whereas the first two series focussed on his dismal attempts to woo her, the couple got engaged at the end of series three, just as Mark realised he didn’t actually love her after all. Much has been made this time of his hope for a way of breaking off the marriage without the social embarrassment of having to tell his fiance he’s no longer interested.

The problem, sadly, is that this is pretty much the only constant this time around, and even this storyline has been given scant time to evolve. From a cracking first episode, in which Sophie takes Mark – and, inexplicably, Jeremy – to meet her parents, our anti-heroes have ended up heading off to a new location every week … usually so that Mark can avoid further contact with Sophie. Indeed, as the story becomes more centred on his dilemma, Jeremy has become sidelined, to the point where his whole appearance in certain episodes has seemed a last minute addition.

If it is a concern that Mark and Jeremy appear to be heading off to new locations every week, then more worrying still is the fact the solitary episode of the series so far that had them travel to their new surroundings in the company of the show’s usual array of supporting characters (Sophie, Johnson, Jeff, and Big Suze all joining them at a Kettering conference), we ended up with probably one of the weakest episodes yet. It seems we can have character-based story-telling, or top class jokes, but not both.

And so we come to the most recent edition. A promising start sees Mark and Sophie visit a relationship councillor, where Mark is appalled to find he is not given an opportunity to subtly exhibit his “subconscious” disinterest in Sophie. A truly great idea – and one that could have filled an episode on its own – however, to the chagrin of both Mark and myself, it quickly degenerated into nothing more than Sophie lamenting his poor performance in the bedroom, before drawing to a swift close.

The main story concerned Jeremy taking Mark on a canal boat stag weekend, with Jeremy’s thoughtfulness about the kind of do his friend would like soon giving way to him forcing Mark into a pub, where he sets his sights on one of two sisters – notably the fifth person Jerem’s been romantically involved with in five episodes. Mark, meanwhile, becomes the object of the other sibling’s desires, but he’s more interested in impressing the father, in the hope of being offered a job in India, ensuing the end of his relationship with Sophie. Yet again, the episode involves importing another entirely new cast of supporting characters, a device that’s starting to become excessive.

However, despite things not looking good, the second half managed to be a comic masterpiece. Immediately before the ad-break, Jeremy runs over and kills the sisters’ beloved dog, and – with he and Mark not wanting this to destroy their carnal or career aspirations respectively – set about trying to destroy the evidence. This culminates in Jeremy coming close to a nervous breakdown as he is forced to eat the burnt remains of the animal’s leg after lying it was a piece of badly cooked turkey. All in all, it turned into an even-more-warped version of One Foot in the Grave‘s frozen cat or incinerated tortoise incidents.

Being Peep Show, it almost can’t fail to include some superb lines, such as Mark’s observation of his new admirer, “Wealthy, lovely family – if only she weren’t such a horrible person, she’d be the woman of my dreams”, or Jeremy’s advice to, “Stop going on about the Euro; we’re in it now, and there’s nothing you can do about it”. The frequent joyous dips into the darkest realms of comedy make me muse that, despite the best efforts of Jack Dee and Ricky Gervais, Peep Show is probably the closest we have to a British Curb Your Enthusiasm. And probably the only other programme to routinely make me weep with laughter.

It seems unbelievable that I should be criticising a sitcom that left tears rolling down my cheeks. The concern is that the show may be starting to run short of ideas and, like The Simpsons, is resorting to uprooting the cast to new locations every week, or introducing an endless array of one-episode characters for the regulars to upset, and then abandon.

I do hope that the next week’s final episode of this run it able to tie up some of these problems, and show us more of the support cast. Mark and Jeremy are wonderful characters, but no sitcom can manage just by thrusting the same two people into a different world each week. Hopefully, the already-commissioned fifth season will focus more on the core cast, who provide the richer array of engaging storylines.

For all the quibbles, however, I can’t stress enough that Peep Show is by far the best sitcom of recent years.