AN unknown poem by Hugh MacDiarmid, regarded as Scotland's greatest poet of the 20th century, reveals he appeared to welcome London's threatened destruction in the Blitz.

The work is among hundreds of previously undiscovered poems found 25 years after MacDiarmid's death scattered through a major collection of his material bought by the National Library of Scotland in 1990 for (pounds) 250,000.

Some 300 in number, they range from epigrams to the London poem and the American bombing of Vietnamese children in the name of freedom one quarter of a century later. In the poem, On The Imminent Destruction Of London, June 1940, he writes of the possible devastation, ''that I hardly care'', and that if any place be ''burned, and lost, it may as well be London - Nay, London far better than most''.

He compares London to a ''foul disease'' and claims ''death and destruction has gone out from London all over the world''.

The collection of unknown poems has been described as wonderful by Dr Alan Riach, general editor of the Complete Works of Hugh MacDiarmid and head of the Scottish Literature department at Glasgow University. They will be included in a new three-volume edition of MacDiarmid's complete poems.

MacDiarmid had worked in London from 1929 to 1932 for what became the Radio Times. Less than a decade later, he was denouncing the city as ''the centre of all reaction to progress and prosperity in human existence'' and seemed to relish the prospect of its destruction. ''What countless shackles must with its shattering shatter,'' he wrote.

The poem still has the capacity to disconcert more than 60 years after the Blitz. It is inconceivable that such verses could have been published during the second world war. It may be MacDiarmid held this piece and others back during his lifetime to protect his reputation.

The parent archive of MacDiarmid material, consisting of 246 separate items, including notebooks, manuscripts and family letters, was sold to the National Library 12 years after his death by the Perthshire-based literary collectors, Kulgin Duval and Colin Hamilton. They had been long-term patrons of various Scottish poets, including MacDiarmid, buying manuscripts from him.

John Manson, a Dum-friesshire-based admirer of MacDiarmid, has assembled the unknown poems, some scribbled in notebooks or backs of envelopes, or embedded in longer works.

Manson, himself a poet, started his research to resolve the question of MacDiarmid's political views, which were inconsistently both Scottish nationalist and communist. He kept encountering poems in the course of his reading and decided to note every one. The 300 finds are the result, with more promised.