Trending: Where rhyme and reason part company

Günter Grass is the heart and conscience of German literature. Grim-faced, Nietschze-moustached, pipe-smoking and combative, the Nobel-winning author of Dog Years and The Tin Drum, has such a starry reputation, it eclipses the fact that he served in the Waffen-SS during the war. You'd think, at 84, he'd be taking it easy. Instead, he's managed to scandalise the international community, to be accused of anti-Semitism and to be barred from entering Israel.

The reason is a poem called "What Must Be Said," a polemic that criticises Germany for exporting to Israel a submarine equipped with nuclear warheads, and warns that Israel may use them as a first strike against Iran. As a letter to his countrymen, it has a polemical force; as a personal wrestle with guilt about being anti-Semitic, it's interesting – but as a poem it's astonishingly prosaic: "I've broken my silence/ because I'm sick of the West's hypocrisy; /and I hope too that many may be freed/ from their silence, may demand/ that those responsible for the open danger we face renounce the use of force,/ may insist that the governments of/ both Iran and Israel allow an international authority free and open inspection of/ the nuclear potential and capability of both."

There have, in the past, been politicians who were also successful writers (Milton, Marvell, Sidney, Disraeli, er, Jeffrey Archer) but it's a curious fact that engaging with politics often sees writers come a cropper. Grass's Tin Drum was an overtly political study of wartime Germany, but the theme was leavened with myth, allegory, religion and folklore. Choosing directness and poetry was a bad idea. The same problem bedevilled Harold Pinter, the great playwright. He wrote about American warmongering with a brutal frankness that never worked. One poem called "Democracy" read: "There's no escape./ The big pricks are out./ They'll fuck everything in sight. /Watch your back." They inspired Craig Brown's parodies, from which they are often indistinguishable.

The former Poet Laureate, Andrew Motion, hit a wall when he published "Causa Belli," criticising the Iraq war, contrasting what's said by pro-war politicians and what's understood by ordinary people: "They read good books, and quote, but never learn/ a language other than the scream of rocket-burn./ Our straighter talk is drowned but ironclad:/ elections, money, empire, oil and Dad." Its simplistic quality enraged American commentators. Several offered alternative versions: "They buy my books, and say, This stuff is shite/ But that doesn't stop me preening, or dashing off more tripe/ Once you're Poet Laureate, you can never get the sack./ The only way to shut me up is to invade Iraq."

Ian McEwan's reputation took a nose-dive in 1982 when he wrote an oratorio for the composer Michael Berkeley: it had an anti-nuclear warfare theme, and climaxed with: "Will there be womanish times/ Or shall we die?" Martin Amis also wrung his hands about the proliferation of nuclear weapons in Einstein's Monsters in 1988, where he described rocket warheads as resembling hellhounds at a children's tea party. It's among his least regarded works.

The moral seems to be: unless prepared to embed themselves in conflict zones or to confront politicians head-on, writers are well advised to avoid making topical political points (especially in verse) for fear of seeming tendentious. There's nothing worse for a writer's reputation than to sound as if he or she has just dashed off a jolly cross diatribe on current affairs to the Letters page of their daily newspaper.