By Rebecca Thomas BBC News Online entertainment staff

There is no novelty in a West End play boasting a Hollywood actor in the lead.

But in serving up two for the price of one, On An Average Day offers a better deal than most.

Add to the fact that the celebrities in question - Woody Harrelson and Kyle MacLachlan - are two of the most individual and enigmatic of the breed and there would seem to be nothing to lose.

Oh, then, what a lamentable waste of opportunity this play is.

Harrelson's character begins to irritate

Though the star quality of this duo is glaring from their first steps onto the stage, they are, from then on, horribly let down by the script.

It prevents either from demonstrating his full ability and squanders the emotion that the storyline makes clear is there to be tapped.

The scenario for this dramatic calamity is the reunion of two estranged brothers and is set in rural upstate New York.

Older sibling Jack, played by MacLachlan, unexpectedly returns to the family home after a 15-year absence.

He finds his abandoned younger brother, Robert, played by Harrelson, living a solitary and tormented existence.

Robert has no money, no food and has something obnoxious rotting in the fridge.

An obsessive disorder compels him to hoard newspapers.

In addition, it emerges that Robert is facing trial for seriously injuring a man by pushing him out of a moving car.

Harrelson acts his socks off trying to make the most of his character

Robert is evidently far from sound of mind and - not surprisingly - does not so much as engage in conversation with Jack as embark on an incontrollable, yet affectionate, rant.

During the course of this verbal onslaught it somehow becomes clear that the cause of this mental instability is the father that deserted the boys when very young.

Robert lives in a perpetually infantile state, waiting and believing this man - and symbol of stability and security - will come home.

And Jack, though affecting calm, has not - as it turns out - escaped unscathed and carries his own terrible demons through life.

Harrelson has made his name by taking on courageous, offbeat roles.

Though best known for Woody in US sitcom Cheers, he also played the disturbed protagonist of Natural Born Killers.

MacLachlan's role is just as a sounding board

It is not difficult, therefore, to see what might have attracted him to the role of Robert.

But you can not help but feel that Harrelson has been severely let down.

Yes, Robert is pitiful and, yes, playing his manic jack-in-the-box character demands great energy and skill.

But, for all that, Robert fails to engage our sympathy, loses our interest and becomes hugely irritating.

Harrelson acts his socks off trying to make the most of his character but there is little cohesion to his ramblings that just go on and on.

Robert and his verbal diarrhoea dominate up to three-quarters of this play - and that is where the biggest problem lies - MacLachlan's Jack is virtually frozen out.

Even given MacLachlan's back catalogue of slick, thoughtful roles - such as FBI agent Dale Cooper in Twin Peaks - his lack of vocabulary here is frankly disappointing.

For much of the play, Jack is just a sounding board for Robert and an incentive for him to dig deeper and deeper into the pain of his past.

The misuse of MacLachlan's talent is a crying shame and one that becomes increasingly frustrating.

Only in the final throes of the play does MacLachlan get to see some of the action and engage in proper dialogue and display powerful emotion.

Then, and only then, does this play and its classy actors show their true potential, becoming in the process totally absorbing and almost too pitiful too watch.

On An Average Day is on at the Comedy Theatre in London.