A good man is hard to find, they say. But with the adoption of the BBC foreign correspondent Martin Bell to stand against the Conservative Neil Hamilton for the seat of Tatton, in Cheshire, it seems one has been discovered after all. Who knows, he might even overturn a sizeable majority. As they also say, you can't keep a good man down.

Mr Bell's being unaffiliated is part of what makes him good. Though they approve of him, he stands neither for Labour nor the Liberal Democrats but as an "anti-sleaze" candidate opposed to corruption in public life. No doubt he has opinions on other matters. But for now his raison d'etre is to spread a little wholesomeness, to shine as a good deed in a naughty world. Welcome to the Virtue Party.

Most journalists have found all this a little awkward. However deeply they loathe Mr Hamilton, they're not used to seeing one of their own cast in the role of saint. Journalism, after all, is as tainted a profession as politics, and had Martin Bell not spent most of his career as a foreign correspondent it's hard to imagine him getting the chance to be Holier than Thou in Tatton. These days, only the far-flung Bells and Kate Adies and Mark Tullys and John Simpsons have much of a reputation for integrity. We know they're courageous, because we see them in the firing line, sometimes literally; we know they're good, because the enemies they report on - war, famine and tyranny - are so obviously evil. Whereas home journalists can't help but be worldly, consorting with and even resorting to sleaze in order to report it, those who bring us world news gleam with innocence.

It's not just journalists, however, who feel awkward in the presence of Virtue. "Is he a good man?" isn't a question most of us would ever ask around a dinner table or in ordinary conversation. "Is he a nice man?", yes, but that's to ascertain if a chap's sociable, clubbable, "one of us", not, heaven forbid, if his soul is pure.

But with Martin Bell's adoption, the question is unavoidable: What is a good man? Embarrassing though it is, I asked it of several people last week. The answers ranged from the solemn ("Someone who puts friends first") to the sporting ("Someone like Robbie Fowler, telling the referee it shouldn't have been a penalty"), from the spiritual ("Someone with compassion for the needs of strangers") to the fleshly ("Someone who talks to you before, doesn't grunt too much during, and offers you a cigarette after"). Some respondents thought that "good" and "bad" were meaningless abstractions - that a man might tell lies, for example (to spare pain), or even kill someone (a tyrant) and yet clearly be on the side of the angels. Others, thinking perhaps of Oskar Schindler, wondered if a man doing good from dubious motives (vanity, say, or greed) could still be irreproachable. Nearly everyone wondered if "a good woman" had different connotations (yes, more domestic ones) and questioned whether the word "man" could be used to stand for "person" (probably not). But no one seemed at all confident as to what the phrase "a good man" might mean.

It's a while, certainly, since it had any currency. Used in an RAF mess, say, by a group of exhausted pilots discussing the merits of the latest recruit, circa 1941, "a good man" would have denoted soundness, courage, dependability. The military context seems inescapable. The Greek word for virtue, arete, was associated with valour in battle; the Latin word virtus connotes manliness, of a Clint Eastwood kind.

But in a country that has been at peace for more than half a century, what's expected of a good man has surely changed. Intellectual courage is more esteemed than physical now. Loyalty to a transforming social idea is perceived as dangerous, as it wasn't in the 1930s; better to be loyal to those you love. And if you have children, you're expected to spend more time with them than your father did with you.

The performing of charitable acts comes low on the list, so my anecdotal social inquiry suggests. "Do-gooder" has come to be a pejorative term, now that philanthropy is regarded with suspicion, as an ego- or power- trip. Affiliation to church doesn't count for much either: what people want is "good, but not religious good", to use a distinction from Thomas Hardy's Under the Greenwood Tree. Passive or contemplative virtue is useless, a light hidden under a bushel. Men can't be good unless they put themselves about, in the common run - just as politicians can't be trusted unless they sometimes ride on buses.

Hypocrisy remains incompatible with goodness. But several respondents pointed out that men diligent in their public duties yet messy and dishonest in their private lives aren't necessarily hypocritical: one can be a good worker and yet a bad husband, dependable in the one role but not the other. These are grey areas, and grey times. Doris Lessing once published a novel called The Good Terrorist, a contradiction in terms until you think of Nelson Mandela and the ANC, or even of Eamon Collins, the IRA member now belatedly atoning through a book. As black can shade to white, so white can shade to black. Even Chekhov, the good doctor, doesn't look quite so unimpeachable nowadays as David Hare points out in the introduction to his adaptation of Ivanov.

So what is a good man? However hesitant those I talked to were to speak them, in the end the same few words kept coming up: courage, loyalty, honesty, kindness to others. More interesting than the question of whether Martin Bell is "good" in this way (and even now, some enterprising soul will be sifting his past for grime) is whether these are qualities necessary to a good politician. Neil Hamilton's reaction, on meeting Mr Bell, was to say: "He seems like a nice guy - totally unfitted for politics."

This is the kind of remark we've come to associate with Mr Hamilton, who takes the biscuit for cynicism. But let's not be pious: most people feel the same. To get on in politics should not require bribery and corruption, but it will require manipulativeness, ambition, ruthless cunning and self- interest. For four weeks every five years or so, the politician must conceal these qualities and impersonate a good person. He must smile, shake hands with strangers and answer a lot of damn-fool questions in order to have five more years in office behaving just as badly as he always did.

Knowing this to be so, the great majority of people regard election campaigns with at best scepticism and at worst contempt. When we come to vote, it's in the hope of electing not a good MP, but a good-enough MP, whom we judge for how he or she handles local issues, not national ones. As for Westminster, most of us are pleased to see at least some members who're naughty but fun, who can add what Hazlitt called "the spice of mischief" to the brew. When Alan Clark was adopted as candidate for Kensington and Chelsea, there was widespread delight at the prospect of having him back in the Commons; even some Labour stalwarts secretly hope he will win.

But what's attractive in Alan Clark, apart from his wit and impudence, is that he knows when he is being bad. Neil Hamilton, by contrast, goes on believing, against all the evidence, that he is good, or that his not being good doesn't much matter - and wants us to believe it, too. He is all dark crannies and professional smarm, which is the point in setting a non-politician against him, to expose him to the common light.

"Virtue," said Diderot, "is praised but hated. People run away from it, for it is ice-cold and in this world you must keep your feet warm." Martin Bell's one-man Virtue Party may be as appealing as a cold shower. But a time comes when you have to get out of the jacuzzi.