I’m usually woken at 6 by the sound of Catherine’s breast pump. It makes a god-awful noise — a sort of growling that reverberates all over the bedroom. Francis is just three months old and I call him the Nazarene because he’s so good. But I’ve barely uncovered my ears from that noise when screams start emanating from another room, and after five minutes I can bear it no longer. Dora’s three and Senan — named after one of Ireland’s saints — is one. I’ll attempt to bring them both back to bed with me, but I can guarantee that the second I put my head on the pillow they’ll start jumping on top of it. It’s no use.

The day has begun.

I’ll take them downstairs and feed them. It’s a battle and I admit defeat even before I’ve started. We like to give them a cooked breakfast — maybe eggs and bacon —- but half of it will end up on the floor or the walls or any low-lying surfaces. I’m trying to be a bit healthier myself, so I’ll have plain oats with milk, but if I’m lucky a bit of congealed egg or chewed bacon fat will have landed in it. Then my elder daughter, Martha, comes down. She’s 10 and the sensible one. She always thinks ahead —she’s even got a part in Creation, the new film about Darwin.

Suddenly it’s 8, I’ve completely forgotten the time and I’m in a panic because we need to leave to get Dora and Martha to school for 8.30. We moved to a new house in Shepherd’s Bush recently so we’d be within walking distance of everything, but things never turn out quite as you’ve planned. By 8.15 there’s more tears, more dramas, and I end up having to take the car or we’ll be late. Of course, in the rush I nearly run down half the parents and kids going in on their bikes. They look at me as if to say: “Why are you in a car? You live round the corner. You big twit!”

I’ll then head home and write a list of things to do. If I even glance at eBay I’m hooked, so I avoid it like the plague and think up some great DIY plan — there’s nothing like it to give you a sense of your purpose in life. Admittedly, it means wandering round the hardware shop all morning and buying stuff I’m never going to use, but it’s a start. I’ve just changed all the light switches. We used to have these incredibly ugly plastic ones; now we’ve got these incredibly ugly expensive ones.

If I’ve been in any kind of queue I’ll come back in a rage and stomp around the kitchen, getting in the way of Catherine, who’ll be feeding the kids lunch. I’ll end up looking for leftovers or standing by the toaster with a loaf of bread. Then, when the kids go down for their afternoon nap, I’ll go into the study and remind myself that when I’m not faffing around, I act. I’ve usually got scripts to read, or I’m doing research, or maybe rehearsing for something, in which case my whole routine turns upside down. I’m just about to appear in a wonderful play called Life Is a Dream. It’s by the 17th-century Spanish playwright Calderon de la Barca and explores the theme of fate by asking if we can use our free will to shape our destiny.

I love doing theatre, but I’m probably best known for my role as Jimmy McNulty, the Baltimore cop in The Wire. I started doing the first series back in 2002, but then it became a big hit in the States and I ended up going back over there to film four more series. Now it’s over, I need to stay put and be closer to the family. Catherine and I are getting married next June. She’s from Limerick and we met at Trinity, Dublin, where we were both doing Irish literature. I was born in Yorkshire and went to Eton, but I’d grown up with this romantic notion of wanting to live in Ireland because my mum’s family were from there. Studying Joyce and Yeats seemed like the perfect opportunity.

Before I know it, it’s nearly 3.40 and time to pick up Martha. I get on my bike this time and tear out of the house to meet her at the school gates — it’s one of my favourite parts of the day. I’ve tried helping her with her maths, but she clearly knows more about it than I ever did.

Supper is at 5.30 and another food fight starts. We’ll eat with the kids or afterwards, depending on how chaotic it gets, and then it’s bath time. I get less frazzled by this — I don’t know why, because Senan’s usually flooded the floor before I’ve even found the soap.

By 7.30 the kids are hopefully asleep and I can sign off. I’ll go downstairs and drink solidly until midnight: beer, wine, whatever I can get my hands on. The stronger the better. If Catherine and I are staying in, we’ll watch TV or I’ll trudge out in the rain and get a video, which she’ll then fall asleep in front of, and I’ll end up getting fined £50 because I’ve forgotten to take it back. If I’m not too drunk, I’ll get one of Catherine’s milk bags, stick it in the microwave and attempt Francis’s 11 o’clock feed.

If I’m not ready to go to sleep myself, I’ll sit up in bed and hold up this book on Proust that I’ve been trying to finish for the past five years. Then I’ll cuddle up beside my beautiful wife-to-be and wonder how long it will be before a child crawls in between us s

Life Is a Dream opens at the Donmar Warehouse, London, on October 8

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