What's so good about Alan Ayckbourn?

Just about every theatre in the land has heard the "Ayckbourn roar". At least twice it has been so loud it has broken the tannoy system that relays a show to actors awaiting their cues backstage.

And when The Norman Conquests were running in London 30 years ago one man literally fell out of his seat and rolled into the aisle.

So it may seem a bit perverse to say that the essential qualities of Alan Ayckbourn's theatre is not comedy but theatricality and truth. That West End company, led by Tom Courtenay and Penelope Keith, actually had to work to rein the audience in after that – damping the laughs down – to ensure that they stayed with the story, the situation and the unfortunate people thrown together on stage in front of them.

It is the dinner party scene in The Norman Conquests that does the damage. There's a chair shortage. Tom, a dim vet, gets a seat so low that Norman (a librarian trying to seduce all the women in the play, including his own wife) can pretend he's a child.

When somebody else cracks a very bad joke about vets, Norman looks down on Tom and asks if the joke went over his head. Read the play and you would ask: 'What's funny about that?' On stage this mild verbal gag is rocket-fuelled by the physical arrangement that put Michael Gambon on a child's chair. But the real magic ingredient is the accumulated expectancy of an audience which knows there is not enough food to go round, only an excess of homemade wine; that Tom's inability to ask the daughter of the house to join him in a dirty weekend has left the field open to the philandering Norman; that Sarah, Norman's sister-in-law, is permanently on the verge of a nervous breakdown and is desperately trying to keep the meal civilised; that Sarah's husband Reg, a man who can't remember the names of his own children, will jump with both feet into whatever delicate situation is going and that Tom is an amateur boxer.

Soon, ordinary but recognisable people – behaving in extraordinary and often horrible ways – will bring a variety of seriously combustible elements neatly together. The scene borders on the farcical, but it's funny because what these characters will say and do is not only cunningly plotted but truthful.

The three plays which make up The Norman Conquests were written over 30 years ago. In his 70th year – his last as artistic director of the Stephen Joseph Theatre following a major stroke – his demands of himself are a little different.

This week Haunting Julia launches what is now a trilogy of ghost stories. Three men meet in the flat where a student has killed herself. Her father, her former boyfriend and a professional investigator of ghostly matters have a haunting to unravel. But was Julia, a brilliant musician, herself haunted or is she doing the haunting?

Audiences will certainly laugh and they will also be severely jolted by an amazing theatrical moment, but above all they will be drawn into an intense psychological study of three very different men linked by the past.

Later in the summer it will be the turn of the three women who appear in Snake in the Grass and finally in July what is now a trilogy of ghost stories will be complete when three men and three women join forces for Ayckbourn's first play since that stroke, Life and Beth. Under the overall title of Things That Go Bump there will be opportunities to see all three together.

This is the other side of Ayckbourn's theatricality, the ability over half a century to deliver plays that are not only funny but also big events which make a small town on the Yorkshire coast from time to time the epicentre of earthquakes in world drama.

I'm not always sure that Scarborough realises this, which is why it was so gratifying that when the eight-part Intimate Exchanges transferred to Broadway this season it found itself nominated for a string of awards. But no audiences are more sophisticated than Scarborough's when it comes to following experiments in narrative form, thanks to Ayckbourn: apart from Intimate Exchanges, think of the two simultaneous dinner parties in one space in How the Other Half Loves, the love scene half in French in House and Garden, the story unravelling simultaneously backwards and forwards in the underrated Time of My Life. In fact, Scarborough audiences are so used to this that the dread word "experimental" rarely gets used about Ayckbourn. His craftsmanship is so great that we are never lost or even fearful that he may not know what he is doing. But it is also very simply because his plays are true. At the root of all this, I would suggest, is what the embittered old film director in Comic Potential describes as the second secret of comedy (the first is, of course, timing): it is anger.

Ayckbourn was never tagged an Angry Young Man, but as a young writer he was profoundly energised by anger at two things, the way he perceived his mother to have been treated by his stepfather for 10 years and the way young men and women were required by society to make promises (in marriage) they were too young to understand, let alone keep. But in some of his great morality plays, like Way Upstream or A Small Family Business, there is also a specific anger at the way mankind is given the chance to live in paradise but invariably turns it into hell.

Anger is surprisingly creative for comedians: think not just of satire but that phrase "the punch line".

Great actors too – Laurence Olivier for example – sometimes treat the audience as an enemy to be conquered. Their aggression isn't visible, but it's essential.

But anger is also the emotion which allows you to break out of politeness and say the things you really mean. This can be risky in real life, and few people have seen Ayckbourn himself in a rage, but it is astonishingly liberating in the art of playwriting.