But even now, he remains something of an irritant on the British literary scene: the East End Jewish boy turned actor, playwright and social critic who began, back in the late 1950s, by exposing the dark and violent urban underbelly of a post-war Britain still sold on a sunny Ideal Homes image of itself; and who has become ever more politically angry and engaged with advancing age, using his position to champion human rights and freedom of expression in the 1980s, and, in recent years, to denounce British foreign policy in Kosovo and Iraq.

Those who heard Pinter speak openly and movingly, at the 2002 Edinburgh Book Festival, about his recovery from cancer, and the role of his much-loved second wife, Antonia Fraser, in willing him back to health, will have noted a mellowing of the playwright's personal tone; but politically, he remains more radical than ever, a furious dissident against a British government he views with contempt.

What makes Pinter matter as a playwright, though, is that his power to challenge, disturb and reinvent goes far beyond the content of his work, into deep areas of theatrical language and form. Like many great playwrights before him, Pinter began his theatrical career as an actor; and although he was born into the same generation of British playwrights as John Osborne and Arnold Wesker, it soon became obvious that his theatre had little in common with the default-mode naturalism of most English drama, but belonged - for all its seedy atmosphere - to a different realm of symbol, metaphor, carefully sculpted language, and fractured theatrical poetry.

From the outset, in strangely menacing early plays like The Caretaker and The Birthday Party, Pinter handled the theatrical medium with a terrific linguistic energy and experimental confidence that linked him as much to Samuel Beckett and the French absurdist tradition as to other "kitchen sink" British playwrights; and later in his career, as he turned his attention to the plight of the Kurdish people (Mountain Language, 1988) or to the legacy of the holocaust (Ashes To Ashes, 1996) the international character of his work, always implicit in its form and style, became increasingly apparent in its content.

Nor has Pinter ever completely abandoned his career as an actor, which continues even now to inform his extraordinary feel for dialogue, and the fierce precision and dynamism of his language in the mouths of actors. From Joseph Losey's The Servant in 1963 - where Pinter appeared as a "society gentleman" in his own screenplay - to the 1999 film version of Jane Austen's Mansfield Park, in which he gave a memorable performance as Sir Thomas Bertram, he has continued to act both on film and on stage. Only last weekend, he appeared on BBC Radio 3 as one of the performers in his new compilation play, Voices, a musical reinterpretation of themes and fragments from his recent work; and earlier this week, the Royal Court Theatre announced that one of the star attractions of its 50th anniversary season next year will be a solo appearance by Pinter in Beckett's great monologue of old age and lost dreams, Krapp's Last Tape.

Perhaps because of the global influences on his work, as well as the scepticism and wit with which Pinter tends to view British life, the nation's greatest living playwright has rarely been the undisputed toast of the London theatre scene. As his biographer, the critic Michael Billington, pointed out last week, there is no celebration of Pinter's 75th birthday on the English stage this year. But his global reputation continues to grow, particularly in those parts of the English-speaking world where the rich, inventive brilliance of his mongrel theatrical language can be most fully appreciated. The Gate Theatre in Dublin is currently staging a massive celebration of his work. And here in Scotland, Andy Arnold's brilliant little Arches Company in Glasgow is marking the occasion with a superb five-star production of his short plays A Kind Of Alaska and Moonlight, followed - from next weekend - by a revival of Betrayal, his back-to-front 1978 drama about a passionate, failed love affair. As for his famous pauses - well, they are the mark of a great actor-playwright who knows that in theatre, the way words are spoken matters as much as the words themselves; and that the silences carry as much meaning as the dialogue.