Read an exclusive extract from Antony Sher's Year of the Fat Knight

Clapham High Street is a long stretch of mini-supermarkets, hardware shops and scruffy cafés; it's not my favourite place, particularly on a grey day, but this is where the RSC rehearsal rooms are situated: a characterless building with a big open space on each floor. We're on the top.

God, the shows I've done here, I think as I climb the stairs, but the memories – all good, as it happens – provide no protection against the first-day-at-school nerviness that accompanies me into the room. It's ridiculous. I've been an actor for over forty years, yet I'm as anxious today as I was when I started out.

The room is long and high, and large enough to have the footprint of the main Stratford stage marked out on the floor. The tall windows overlook the surrounding buildings, and have black drapes, which have to be drawn when the low December sun slants in, making you shade your eyes. We're moving to a different location in a few weeks, so this is rehearsal room number one.

Actors are arriving, pulling off overcoats, scarves and hats. Most of the cast are strangers to me. I say hello to Alex Hassell (playing Hal): he's got a big open smile, and looks great – tanned from a trip to India. Then I make a beeline for someone I know very well indeed: Jim (Hooper, my former partner, now closest friend), who's playing Silence and Vernon. It's going to be a comfort having him as a travelling companion on the journey ahead.

When everyone's assembled, Greg [Doran] does a brief talk, introducing some key RSC folk: Catherine Mallyon, Jeremy Adams (our producer), and John Wyver (who'll be in charge of our broadcast, Live-from-Stratford). Greg also explains why we're starting on this unlikely date: although we'll lose Wednesday (New Year's Day), it still gains us an extra week. We've got eleven in all, for two plays.

(I'm not convinced that's enough. Greg's argument is that although it's two plays it's only one character – which will speed things up.)
Now Greg says, 'We're going to do a little icebreaking game. Technical team and stage management are welcome to participate, but actors have to.'

As I watch all the non-actors flee for the exits, I think: Games – whether on sporting fields, at parties, or in rehearsals – I hate them!
This one involves us walking around the room, greeting one another, and imparting three facts about ourselves. Then we'll each sit in the hot seat, and the group will try to remember what they've learned about us.

As I stroll round, I tell people I was born in Cape Town, I have a wool allergy, and one other thing which is sure to 'break the ice'.
When we go into the next part of the game, the hot seat, I begin to see the point and pleasure of the exercise: we have, very quickly, got to know one another. Sometimes the facts are trivial – the names of pets or favourite colours – sometimes more important: someone was almost stolen as a baby, someone else fell out of a helicopter.

My turn comes. As soon as I sit in the hot seat, people start to shout out the third fact I told them:
'He's sleeping with the director!'
Greg gives a spluttering laugh: 'You told them that?'
'I did,' I reply; 'I thought it best they knew.'
Josh Richards (playing Bardolph and Glendower) pipes up: 'It's the only reason he got the part!'
'Absolutely true,' I say, and then to Greg: 'Now we're both blushing.'
Much laughter.
(Though there was a time when Josh would have been giving voice to my very real fear.)

Now Greg does a talk about the plays, and about Shakespeare. He's always felt that the RSC needs to help those young actors who are joining for the first time, and who may feel ignorant about our resident playwright. He claims it's how he felt when he arrived as an actor in '87, which I don't quite believe (he was living and breathing Shakespeare as a schoolboy), but it's certainly how I felt back in '82.

He's brought along some books in a canvas bag we got at Shrewsbury, with the logo Battlefield 1403, and lifts out his facsimile of the First Folio. 'Here's my favourite page,' he says, showing the group the list of actors in Shakespeare's company: Richard Burbage, Will Kemp (who probably played Falstaff ) and the rest. Greg relates stories about many of them. We listen, enchanted – we, modern-day actors – basking in their long-ago glory.

'Thank God I don't have to read Falstaff today,' I said to Greg as we gathered round the table for this afternoon's session. He's the only director I know who doesn't do a read-through on the first day. Maybe because he was an actor, and knows how crucifying it can be. We all try to pretend it's not a kind of audition (even though you've already got the part), but judgements are made.

Nevertheless, we do start reading Part I. We go round the circle, each reading whichever part is next, as long as it's not our own – the rule is you can't read your own part – and then 'translating' the speeches into everyday English. We're aided by the notes in the various editions on the table: as well as the ones I've been using – the RSC and the Arden – there is the Oxford, the Pelican, the New Penguin, the New Cambridge, as well as an invaluable bible, the Crystals' Shakespeare's Words: A Glossary and Language Companion.

Some surprises as we proceed. In Act One, Scene Scene, Westmoreland tells of the fate of Mortimer's forces against Glendower; the butchery and mutilation of soldiers:

Such beastly shameless transformation
By those Welshwomen done as may not be
Without much shame retold or spoken of.

We look at one another, frowning in puzzlement. Then Josh Richards, who's Welsh, says, 'I've known a few women like that back home.'

We laugh and are about to move on, when Simon Thorp (playing Blunt and Lord Chief Justice) looks up from his Arden edition, and says there's a note about the mutilations. They involved the cutting off of penises and sticking them in mouths, and the cutting off of noses and sticking them in anuses. Stunned, we turn back to Josh, who says:
'Oh yes, there was this lady in Cardiff…!'

Year of the Fat Knight: The Falstaff Diaries by Antony Sher is out now, published by Nick Hern Books in hardback with colour illustrations. Get your copy for just £11.89 (30% off the rrp of £16.99) – use voucher code FALSTAFFWOS at checkout at nickhernbooks.co.uk. Signed copies also available while stocks last.