Over the course of 50 years, Guardian theatre critic Michael Billington has reviewed over 10,000 productions. He is, joked National Theatre Director Rufus Norris, at tonight’s event: “The critic who’s struck more fear into us than all the other critics put together.”

Norris was – to a large extent – jesting; one of the secrets to Billington’s longevity is his genuine love of theatre, which appeals to artists and audiences alike. Who else could attract actors of the calibre of Simon Russell Beale, Penelope Wilton, Oliver Ford Davies and Aisling Loftus to a farewell event at the National Theatre?

Because Billington really does care about the actors. “It can be difficult to keep a distance”, he admitted, “Especially when you’re dealing with a very young company that’s just starting out; you’re aware that they’re not paid very much and you don’t want to crush them.”

When writing a review, Billington told us, the key is to be honest about your reactions: to analyse them and express them as clearly as possible. As a point of principle, he never reads other critics’ reviews – and has a policy of never discussing a production with a fellow critic on the show’s opening night, although he’ll chat to them about it the following day.

His approach to review writing is to file his copy by 9.30am the morning after is preview which, over recent years, has meant getting up earlier and earlier: one of the reasons behind his forthcoming retirement. Reviews, Billington says, require a certain structure and if you use it the necessary words follow.

The most difficult element of reviewing is having to corral your thoughts into an allotted space; responding to something that comes with no previous history can be equally challenging: “That’s the hardest thing for a critic. You have to avoid embracing it and being over-radical.”

Pressed on whether he “dreads” any particular play – and to guffaws from the audience – Billington admitted to finding the ‘mime’ genre challenging “as well as plays which you’ve seen so many times that it’s hard to summon up another reaction, such as ‘Romeo and Juliet’.” However: “Some plays, such as ‘Hamlet’, you never tire of.”

If you’re lucky enough to see a play for the second, third or fourth time “you see things that you didn’t see originally” – for example, Harold Pinter’s ‘Betrayal’, which Billington famously rubbished following its premiere in 1978. Winningly, he admits to having misjudged it and “I seem to have spent much of my life exploring its complexities. But artists, directors and critics all make mistakes: that’s what makes theatre so interesting.”

‘Betrayal’ has some of the most delicious dialogue you’ll ever encounter and this was illustrated beautifully by Simon Russell Beale and Penelope Wilton’s reading of one its most emotionally-charged scenes.

On the flip side, Billington named last year’s Haymarket Theatre production of David Mamet’s ‘Bitter Wheat’ as the worst show he has ever seen, despite it starring John Malkovich, whom Billington admires greatly: “It had nothing new to say.”

What Billington relishes most about theatre is how it is influenced by the politics of the time, and how it can help propel social change. He cites Terence Rattigan’s ‘The Deep Blue Sea’ as an example; written several years before the ‘Wolfenden Report’ was published, it “…showed which way the public was leaning when its Shaftesbury Avenue audiences gave it a standing ovation night after night.”

Now, as then, theatre reflects the world in which we live and Billington noted how the National Theatre audience is much more diverse than it was ten years ago, because more playwrights from ethnic minorities are achieving success. Last year’s ‘Small Island’ is a good example and I thoroughly enjoyed Aisling Loftus’s reading from the play, to which Billington awarded a rare five-star rating.

Technology, he believes, has to be a friend to theatre – and vice versa: “Theatre cannot avoid the digital world and its rapid evolvement.” It can, however, go wrong, as evinced by Andrew Lloyd Webber’s ‘The Woman in White’: “A rather fine musical let down by its technical aspects.”

Billington doesn’t, however, believe in the argument that theatre criticism is dying. “People said the same about the novel and about film – yet both have survived. What is happening is diversification; reviews are printed on-line as well as in print. Eventually, the two will align.” He argues that both theatre and the audience would be worse off without criticism – pointing out, amusingly, that the most bitter letters he’s ever received are from artists whose work he hasn’t reviewed: “Any artist will tell you that it’s far worse to be ignored.”

Tonight’s insightful encounter, with one of our greatest-ever theatre critics and some of our finest actors ended on a hilarious high when Billington was asked to name his all-time favourite King Lear (both Simon Russell Beale and Oliver Ford Davies have played Shakespeare’s tragic protagonist). Diplomatically, Billington cited Paul Scofield in Peter Brook’s 1962 production, praising the way in which Brook gave the tragedy many moral layers, allowing Goneril and Regan “…not to be simply wicked, but to have a good case against Lear.”

One final fact I learned tonight was that Michael Billington and Oliver Ford Davies studied at Oxford together where they acted in the same productions, “…but Oliver was an actor, and I wasn’t!” Another Oxford contemporary, Ken Loach, often joined them in said productions: “Ken was a very good comic actor – which he’s kept quiet ever since”, deadpanned Ford Davies.

The theatre world will miss Michael Billington, and his quietly devastating reviews, greatly – as will its audiences. Billington bridges the divide between theatre and audience in a way which few critics manage to do. What a legacy he has left behind, however, in making theatre so approachable. We have much to be thankful to him for.