MOST of us have chuckled at the dishevelled, wide-eyed bloke with the straggly hair and matted beard barking in the street.

But Dirty Filthy Love (ITV1 Sunday) forced you to remember that, behind the beard and the penchant for Lassie Sings the Blues, there's a real person.

In this one-off black comedy drama, the wierdie beardie becomes someone we know and care about in the shape of regular guy, Mark Furness, a talented young city architect with a beautiful wife and a nice lifestyle, for whom things went wrong.

It showed how mental illness is just a couple of doors down from all of us and if you happen to be bleaching your eyelids or spraying air-freshener outside the front door at this moment - read on...

As in real life, Mark's slide starts innocuously enough.

He is stressed at work (isn't everybody?) and his marriage to Stevie is suffering as a result. She's trying to keep things together, but he's twitching, scratching and generally acting a bit odd.

Eventually Stevie has enough of his mad behaviour and tells him to sling his hook; then the firm of flash architects he works for informs him that he's one brick more than they need for their next project.

Cue slippery slope and a great exit speech.

Played movingly by watch-this-face actor, Michael Sheen (ex-husband of Kate Beckinsdale, daughter of the late Richard Beckinsdale, triv fans), we see how Mark's increasing sense of failure combined with the added stress of separation and unemployment turns him into a complete basket case, suffering with OCD, obssesive-compulsive disorder.

Tragi-comedy scenes included him swearing like a navvy in really inappropriate situations, being unable to walk up stairs normally and washing himself in the kitchen sink with bleach.

Life's little "habits" suddenly took on a whole new meaning as he tries using the mundane minutiae of life to gain some control over the big things that are going wrong.

So we see him gently fall apart.

Things take a turn, not always for the better when he meets Charlotte, a fellow OCD-er, who immediately recognises his symptoms.

It got a bit clichd then, trying to be a bit Fight Club-ish, with Charlotte (played by Shirley Henderson - Moaning Myrtle in Harry Potter) trying to emulate the quirky Helena Bonham-Carter character from the film and endless, overdone black comedy about therapy sessions and the people who attend them.

But then it settled down to be a quite remarkable drama that was bleakly funny, without ever making its subject matter the butt of the joke.

Mark's mental state deteriorates, and, just for a laugh, his latent Tourettes comes to the fore.

So, we see him roving around town woofing and gaffing all over the place, going from flash-suited city boy to dishevelled, newspaper hugging nutter in the time it takes to say **@@!!!@*!

Unsurprisingly, it's fellow-twitcher Charlotte who comes to the rescue, even though his behaviour and obsession with his ex-wife makes her own OCD symptoms worsen.

And there is a very poignant moment when her wig is pulled off to reveal she's been ripping her hair out from the roots and Mark, hitherto totally wrapped up in his own misery, realises how terribly vulnerable Charlotte is, too.

And so they fall in love, you know the rest.

But it was surprisingly entertaining, while unsanctimoniously giving food for thought.

For instance, I thought that the fact that I lay out the next day's breakfast things (neatly and always in the same positions) before going to bed most nights is just me being organised.

But maybe it means that I'm a control freak, or worse that it's the onset of OCD and by next week I'll be scrubbing my bottom with caustic soda and baying at the (non-existent) moon...

But at least I'll be wearing the correct outfit while doing so (something in a light chiffon perhaps, with a hint of sequins?), now that Trinny and Susannah are back with What Not To Wear BBC1, Wednesday).

There was a time when you could accuse the twittering twosome of pot-calling-kettle-blackism when it came to fashion, especially Susannah, who used to look like early Fergie (Sarah, not Alex - well, come to think of it...) meets county dowager.

But now they're all slick and gorgeous, with Suse in particular looking tres chic. So they're allowed to criticise and thank goodness they did.

Victim number one, Sarah, was okay really. She was just boring and lost and in need of a bit of fluffing up after having recently had triplets and a confidence bypass.

So they reduced her to tears. Nice.

But boy, did Michalinea need help.

A technicoloured hobbit wearing every fashion faux pas possible - leggings, turquoise, top-knot, fake tan, giant hoop earrings.

Where to start?

Well, insults are always a good start: "You're an embarrassment, staid, a little lollipop, a triangle with legs, you scare me."

And that was just for starters.

How these two don't get decked is beyond me, but the results were impressive.

Sarah was able to attend functions with her husband, now she was brave enough to wear a dress.

And good old Michalinea's mates wept tears of joy on seeing that she'd been surgically removed from her shell suit.

Aaah, bless.