Former Times theatre critic Benedict Nightingale is among the judges of this year's Bruntwood Prize for playwriting, entries for which close on 3 June. Here, he tells Whatsonstage.com what he's looking for...

As one of the Bruntwood judges, would I say what I'm looking for in a winner? That's the question I've been posed but find hard to answer, mainly because I'm hoping to come across a play that surprises me by its refusal to meet some predetermined criterion.

After all, who could have predicted Osborne's Look Back in Anger or Pinter's Birthday Party when they introduced their authors to the London stage - receiving, incidentally, some very dodgy and in the latter case killer reviews?

So I guess I'm talking about an X-factor which lifts a play above the customary or conventional. I guess I'm talking about originality or, rather, a dramatic voice that feels unique or at least distinctive. I've seen many highly successful and even prize-winning plays that fail such a test. Reviewing in London for the New Statesman in the 1970s, I wearied of work that worthily, decently, earnestly but unadventurously addressed the nation's social problems. Reviewing in America for the New York Times in the 1980s, I felt much the same about inward-looking domestic plays that always seemed to involve the tribulations of parents and their adult children and often rose to a crescendo of reconciliation on the back porch.

Nothing wrong with either genre as such, but all too often that X-factor, that special slant, that fresh voice, that idiosyncratic way of looking at people and recording their dialogue in striking ways, was lacking. Sorry I can't be more specific - but it seems to me that somewhere here is the challenge that Bruntwood candidates face.

Well, maybe I can be a bit more specific about distinctive playwrights I've reviewed at or near the point of their arrival. Osborne: passionate anger raised to scorchingly eloquent rhetoric. Pinter: the evasive words and frequent silences of embattled, wary people who seldom say what they mean or mean what they say. The Stoppard of Jumpers and Travesties: crazy connections, comic exuberance, all becoming part of an intellectual debate that isn't just for intellectuals. The Trevor Griffiths of Comedians: a highly imaginative and brilliantly worked metaphor for a debate about political stasis and political change. Mamet: bracing, swaggering and often gaudy dialogue that manages to be realistic yet almost poetic as it bring to unmistakable life places as ordinary as a junk shop or a real-estate office. Martin McDonagh: human insensitivity, cruelty, even barbarity seen through a moral lens yet daringly rendered hilarious.

Oh yes, and it goes without saying that any winning play should speak to us, now. That needn't mean being obviously topical. A play can be set in 13,000 BC and still say something that strikes us as pertinent about people, relationships, social situations, even politics in 2013. But I think I'd find it hard to get excited about a play that, however capably and entertainingly, involves the past and only the past. And, yes, that's what I'm hoping for: to be excited by a writer who tells me about my world in a fresh, distinctive, riveting way.

Equally, it goes without saying that any such play must be theatrical or potentially theatrical. I daresay I'd have thought Shelley's Prometheus Unbound very original, very striking, but I hope I'd have known that it, like many plays by great poets, would need an auteur combining the strengths of Robert Lepage and Calixto Bieito to make it begin to come alive.

Distinguishing between a script and a production, especially a first production, is often challenging for critics. Imagining a potential production for a given script is equally challenging for Bruntwood judges - but we need to feel that a dramatist has a sense of the stage. Obvious hint: trust your actors, trust your director, don't present them with dialogue that spells out things too much. Know that less is often more.

Again, one should feel the stakes are high. That needn't mean some sort of tragic circumstance needs to threaten the characters. But an audience must be made to care, even if it's only the fate of some very ordinary individual that is at issue or even if the chosen genre is comic. One of the best plays I've ever reviewed is Brian Friel's Dancing at Lughnasa - five sisters living in Irish obscurity with their maddish brother. We laughed a lot, but, yes, we did care when we learned that two of them moved to London and became down-and-outs. We cared about them all, because of the depth and quality of Friel's own caring.

Finally, I'm asked if it's good that there's now no age limit on Bruntwood entrants and potential winners. Of course it's good. It's not just that ageism is wrong per se: it's also that the country isn't so replete with fine drama that we can afford to exclude any that appears from any human source, whether a seven or 70-year-old. And we're supposedly living longer. Why couldn't a 70-year-old produce a winning play and go to produce others before the grim reaper carries him or her off?

For more on the 2013 Bruntwood Prize, visit www.writeaplay.co.uk