LET us go then, you and I, back to a November night in 1985.

The scene is a tenement on Edinburgh's north side; the occasion the 75th birthday of Norman MacCaig. We are in the sitting room of the flat in Leamington Terrace where MacCaig lived with his wife Isabel. Among the company are the singer Adam McNaughtan, the poets Iain Crichton Smith, Liz Lochhead, Sorley MacLean and Aonghas Macneacail, the publisher Callum Macdonald, and me doing my best impression of a fly on the wall.

On opposite sides of the fireplace sit MacCaig - fag in one hand, whisky in the other - and Seamus Heaney, who has opted for the floor sure in the knowledge that he would eventually end up there anyway. Heaney, nearly 30 years MacCaig's junior, is in listening mode. He had arrived earlier in the day from Dublin to read at the Queen's Hall and, job done and done well, he is happy to sip and savour the conversation.

Theirs was a relationship built on mutual respect and love, first forged at a party in Wicklow, not long after Heaney, then 35, published his collection North, in which he raged in his eloquent and well-tempered manner against the violence that was tearing Ireland apart. It was a place, he wrote, "where bad news is no longer news", "where zoom lenses, recorders and coiled leads/Litter the hotels. The times are out of joint."

"I can't stand gloomy, ambitious poetry," MacCaig told him. "So I suppose Robert Herrick is the one for you, Norman," riposted Heaney. Herrick, a 17th-century English lyric poet, is renowned for his rusticity. "I date our friendship from that moment," Heaney told me four years ago.

He was eager to talk about what Scotland and Scottish poetry had meant to him. He'd won the Nobel Prize for Literature in 1995, which made him even more famous and much busier. "No" seemed to be one of the few words he did not have in his vocabulary. But among the honorifics he was eager to embrace was that of honorary president of the Scottish Poetry Library. Poetry was his be-all and end-all and he knew poems and poets past and present intimately. I never met anyone who could quote so freely and accurately. Were there a poetry Olympics, he'd have been its Usain Bolt.

Once, he told me, in the 1960s, he'd encountered Hugh MacDiarmid in Ireland. MacDiarmid, he recalled, "was a major European poet who said 'och' and smoked a pipe and sounded like your farmer ­cousins." Heaney, who was then based in Belfast, chanted lines from MacDiarmid's poem With the Herring Fishers, demonstrating that whatever damage a recent stroke had done, it had not affected his memory: "For this is the way that God sees life,/ The haill jing-bang o's appearin'/Up ower frae the edge o' naethingness .../It's his happy cries I'm hearin'."

Accompanied among others by Trevor Royle, then literature director of the Scottish Arts Council and now the Sunday Herald's associate editor, Heaney visited MacDiarmid at Brownsbank, his cottage near Langholm. "We drank a lot of whisky that afternoon," he said. "I always remember when we were going to get up out of our seats MacDiarmid was sitting quite spry, saying 'can you manage?'" In Dublin in 1967, when MacDiarmid was 75, Heaney recalled him chasing his pregnant wife Marie round the table with goodness knows what object in mind. He shook his head - partly, one imagined, in wonder, partly in admiration.

In Scotland, he felt very much at home. I heard him read in Aberdeen and St Andrews, and lecture on Sorley MacLean at the Book Festival. He was a great anecdotalist and could hypnotise with a story that he had honed over the years as if it were a poem. He travelled to Stromness to meet George Mackay Brown. At the request of Joy Hendry, editor of Chapman magazine, he translated MacLean's epic poem Hallaig from the Gaelic. He met MacLean, whose eccentricity was legendary, on several occasions, once in Kilkenny, where Sorley accidentally locked himself in his hotel room.

But it was with MacCaig with whom Heaney forged the strongest bond. The first poem he wrote after winning the Nobel Prize was addressed to his Scottish soulmate. Titled A Norman Smile, it opens: "To be marvellously yourself, like the river water." "The muses," Heaney said, that familiar twinkle of mischief in his eye, "were instructing me, I thought, to be myself, not to go with something oceanic and tidal and super-Nobelish, but to stay fresh and true to the old channels."

Of that his old friend would undoubtedly agree, and so it seems appropriate to repay the compliment. These last words come from MacCaig's Praise of a Man: "The beneficent lights dim/but don't vanish. The razory edges/dull, but still cut. He's gone: but you can see/his tracks still, in the snow of the world."