I don't know who it is who makes up the studio audiences for sitcoms or what they're injected with before the recording begins, but, as Ben Elton's The Wright Way demonstrated last week, there is virtually nothing that they won't laugh at. Like laboratory animals trained to respond to some arbitrary stimulus, they react to anything that is even vaguely punch-line shaped. This turns out to be quite handy in Vicious, which is full of lines that have the cadence of comedy but often prove to be devoid of wit when examined more closely.

Or to employ a wit so dubious that an appalled silence might be a more reasonable response. An example: "You let a complete stranger use your loo?" says Frances de la Tour's character when she discovers that Freddie and Stuart's lavatory is occupied. "What if he comes out and rapes me?" Gales... no... tornadoes of laughter.

The basic schtick in Vicious is high-camp bitchiness, a form that reached an apogee in the American sitcom Will & Grace (on which Gary Janetti also worked). This is a sadly depleted version, though, and it's delivered by McKellen and Jacobi as if they're playing in Wembley Stadium and only the upper tiers are occupied, with a heavily semaphored effeminacy that seems to belong to an entirely different era.

That is partly the point, of course - they're supposed to be social fossils - but unfortunately nothing else in Vicious provides a believable backdrop for their self-dramatisations, from the inexplicable eagerness of the young straight neighbour to insert himself into their lives, to the jerky clockwork of the plot. Only Marcia Warren comes out of it with her dignity intact, as an absent-minded friend. Seems almost blasphemous to say it but McKellen and Jacobi should watch her and take some notes on comic acting.

ITV is pushing to invest in primetime comedy again, with loads more Benidorm in the pipeline, as well as two brand-new sitcoms tonight (see also The Job Lot). And they couldn't be more different in style. Vicious is the more old-fashioned - studio audience, huge sitting-room with front door, left, and swing-door to kitchen, right (it's The Golden Girls' format) - except that, in a très moderne move, the central figures are two gay guys.

Actorly ham Freddie (Ian McKellen) and swishy Stuart (Derek Jacobi) have been cattily in love for 48 years. While activists might cavil over stereotyping, there's no denying that the spectacle of two of our finest knights of the theatre camping it up is absolutely hilarious. Along with Frances de la Tour as their voracious mate, Violet, they make every line a zinger. Creators Gary Janetti (Will & Grace, Family Guy) and Mark Ravenhill (fruity West End plays) have a sure-fire hit on their hands.

Relishing the chance to camp it up, old queen style, thespian legends Ian McKellen and Derek Jacobi team up as delightfully tart couple Freddie and Stuart for this theatrical new sitcom. There's something of the retro spirit of Rising Damp about Vicious, with its waspish wit and twilit interior - the fabulous Frances de la Tour is even on hand as fag hag Violet. Tickling the trio's sensibilities is young flat-hunter Ash (Iwan Rheon) who stirs Freddie's gaydar - which clearly needs a 21st-century upgrade - and to get the party started there's a wake in honour of an old friend who, naturally, had a massive crush on the self-obsessed Freddie.

Ian McKellen and Derek Jacobi have a ball as a bitching couple living in a cobwebbed, sepulchral flat, lusting after hunky new neighbour Iwan Rheon, confiding in best friend Frances De La Tour and hamming it up wherever possible. It's a very traditional studio sitcom setup, made watchable by its stars and enjoyable by a waspish script. Also, in its combination of old age and homosexuality, it could be argued to have broken a little ground. Not that creators Mark Ravenhill and Gary Janetti much care about that: this show is all about low blows and easy laughs - at which it excels.

Derek Jacobi and Ian McKellen are Stuart and Freddie, a bitchy, bitter couple holed up in their dingy London flat. In this first episode, the pair become fixated with a handsome young neighbour, as does their brazen friend Violet (Frances de la Tour). With all the very loud talking and theatrical self-pity, this could have been a superbly camp sitcom, but the characters aren't nearly outrageous or monstrous enough. That is clear from their pedestrian put-downs: "At least I'm not from Leytonstone," being Freddie's stock comeback.

If you want to watch a couple of knights slinging bitchy dialogue at each other, Monday nights now offer a surprising alternative to Game Of Thrones.

Sir Ian McKellen and Sir Derek Jacobi star in this fabulous new sitcom which is, believe it or not, even better than the trailers promised.

Together for nearly half a century, Freddie and Stuart are like an old married couple, bound together by their mutual dislike. But they love each other really, of course. I think.

Every line is a belter, which is absolutely what you'd expect when you find out its creators are American Gary Janetti (writer and producer of Will & Grace[/o] and one of the [i]Family Guy writing team) and playwright Mark Ravenhill, who once said he'd be happy never to write another gay character again. I'm glad he changed his mind.

While gay relationships have long been just another part of the furniture on TV, there's never been one like Freddie and Stuart's and certainly not one so perfectly acted.

Frances de la Tour, who plays their friend - would-be maneater Violet - is something of a revelation too. It's taken 35 years but she's finally got another TV role as memorable as her Miss Jones from Rising Damp.

Young Iwan Rheon (Misfits, Games Of Thrones) is set to brighten up all their lives when he moves in to the flat upstairs.

Frances de la Tour - 'I'm going to work until I drop'

"It won't be a question of whether I will give up work, it will give me up. I'd like to just keep going, even if it's just a tiny part of an old lady in whatever it is"

The humour may not exactly be top drawer, but the cast list of ITV's latest stab at primetime comedy can't be argued with. Sir Ian McKellen - Gandalf! Magneto! - and Sir Derek Jacobi - Claudius! The Master! - together... surely it can't be that bad?!

The Sirs play geriatric gay couple Freddie and Stuart, who in this opening episode decide to throw a camp and catty wake for their recently deceased friend. Gurning Misfits actor Iwan Rheon also appears as sprightly leather jacket fan Ash, who's just moved in upstairs, while another acting heavyweight Frances de la Tour plays the couple's ravenous friend Violet. The jokes are groan-worthy, clichéd and occasionally offensive, so we don't expect everyone to come away from Vicious having loved it, but legends like McKellen and Jacobi cosying up together on the same sofa just has to be seen...

A studio-bound, single-set, multi-camera sitcom, Vicious is a gratifyingly old-school farce in which thespian deities Sir Ian McKellen and Sir Derek Jacobi have a char-grilled whale of a time as an incessantly bickering homosexual couple. Sealed within their sepulchral Covent Garden abode - they shriek like vampires when the curtains are accidentally opened - pompous actor Freddie (McKellen) and retired bar manager Stuart (Jacobi) tussle waspishly over decades of perceived slights, while never missing an opportunity to mock each other's supposed decrepitude.

Now, these are hardly original comic creations - the vituperative, hammy old queen has long been a staple of popular culture - and there is nothing especially notable about the premise. But that simply doesn't matter when the execution is as strong as this.

Resembling a startled, wounded guinea pig, Jacobi squeals and frets amidst a knowing flurry of camp mannerisms, while McKellen booms fresh insults in that oak-lined voice of his. He also pulls some of the funniest "Why, I've never been so insulted in my life!" expressions this side of imperial phase Frankie Howerd. It's an impeccable dual assault of seasoned comic timing.

Enjoyment is magnified by the addition of Frances de la Tour as their dotty, man-hungry pal. Famously, she starred in Rising Damp, one of ITV's few great sitcoms, and it's tempting to view her presence here as a deliberate nod to the past. Not that her involvement is merely symbolic - she's a peerless comic actress - but you could argue that she's essentially playing lonely Miss Jones 30 years on. Even the dingy brown set recalls her most celebrated role.

Broad and boisterous in the best possible sense (ie it's nothing like that avalanche of horror, Mrs Brown's Boys), Vicious is jam-packed with gags, hitting the ground running with an impressive opening episode which establishes set-up, character and backstory with consummate ease.

A co-write between acclaimed playwright Mark Ravenhill and Gary Janetti, a former executive producer on Family Guy and Will & Grace, it revels in its camp bluster with such benign relish, I doubt it'll get into too much trouble for reinforcing stereotypes. It's obvious that Freddie and Stuart are blissfully happy in their enmity, and it's that undercurrent of warmth - the spoonful of sugar beneath the barrel-load of bile - that make these characters so engaging.

I'm no soothsayer - I've never said "sooth" in my life - but I predict that Vicious will be huge. A hit sitcom! On ITV! Nurse, the smelling salts...