Jemima Rooper's diary

I have sacrificed my barnet all in the name of art. It looks a little bit like a swimming cap made of hair. My fellow cast members at the National Theatre are very kind. They say I remind them of Winona Ryder, or Demi Moore in Ghost (I'm wearing an oversized shirt when they say this but am not on a pottery wheel, slathered in clay, listening to 'Unchained Melody'). According to our leading man James Corden, I look uncannily like Justin Bieber.

Vanity aside, in my sharp suit by Chris Kerr of Berwick Street, and under the Lyttelton stage lights, I look like a pretty weird short bloke. And that's what we want as I'm playing a girl dressed as her dead brother in One Man, Two Guvnors. There comes a point, especially with comedy, when being in the rehearsal room is no longer helpful. Me giggling at Oliver Chris doing something rude with a sock is not necessarily conducive to discovering what an audience will find amusing. So before getting into the theatre, our director Nicholas Hytner threw open the rehearsal-room doors and invited a small number of drama students to watch us so we could hear their response. It was full-on and wonderful, but it could not have prepared us for the reaction that greeted us on the first preview night. Cast and crew have worked their little socks off and we have a joyous, glorious, ridiculous theatrical experience on our hands. It may be received differently every night, but since making it through the previews and opening properly on the 24th, the atmosphere at the shows has been like a raucous party.

Opening the play would have felt marginally easier if James Corden had not insisted on taking the entire cast out for dinner the night before we got on to the stage. We had a stupendously gorgeous meal at Polpo on Beak Street; wine and food was flowing as well as excuses for our gluttony - 'I need this bucket of wine to relax, I'm soooo stressed!' 'What if my sideburns fall off on stage?' - and thus our first stagger through the technical session was slightly marred by throbbing headaches and rising bile. Some of the more professional members of our cast peeled off after dinner, but the rest of us were taken by James to The Box for more drinks and some crazy cabaret. It remains a blur to me (I understand I was trying to dance on as many surfaces as possible) but there was definite nudity. And probably some fire. I'd like to claim that it was all in the name of research as our show is rooted in end-of-the-pier tradition and is a brilliant reworking by Richard Bean of the Goldoni play The Servant of Two Masters, a fine example of Commedia dell'Arte and thus not a million miles away from what we were watching. But I'd be lying.

Before we started rehearsals I popped over to New York to visit my favourite freckly friend Tom Riley, who is in Arcadia on Broadway. As a born and bred Londoner, New York is pretty much the only other place I could see myself living. On our last day we treated ourselves to a burger and fries from Shake Shack before storming the Met and ignoring all the modern art in favour of the African stuff, which was very phallic and entertaining.

I think smugness is ugly but I can't help it when I'm spending my summer on the South Bank. I still get a swell of happiness when I walk over Waterloo Bridge to work and see the little beach that has been built along the river and all the posters advertising the Hayward Gallery and Festival Hall and people milling around enjoying it all. It's like going to a very fun office every day. Yet another wonderful aspect of getting to work at the National is that our show will share the theatre with another show opening in July and we get nearly a fortnight off. This is scoring me major good-girlfriend points as it means I'm able to go to the Latitude Festival this summer. My boyfriend Ben Ockrent is writing a play called Carrot for Theatre503. I've never been able to attend the festival before but there's a brilliant music line-up (Foals, The National, Lykke Li) as well as shows and cabarets and a Q&A with Steve Coogan and Rob Brydon about The Trip. Enough to get me in a tent for a few nights anyway.

While trying not to be sick on my colleagues (nerves, not hangover, promise) and open a show, I am also, rather stupidly, trying to move house. My boyfriend and I have found a place in Archway, near to St John's Tavern where I can stuff my face with their posh Scotch eggs, but until then I have to move myself with my two weird cats into his place. I also have to fix my Nissan Figaro's rusty bottom, which I hope is no reflection on its owner's. But then this is all good as it balances out my smugness and brings me back down to earth, where I belong.