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At the beginning of the shoot for this two-part episode of Holby City, Time and Tide, I think the director was in some pain. When he was told that we were having two episodes about a flood but we weren't doing any flood sequences, he replied "Riiiiigggggghhhht."

But I think it all works pretty well. It was a pretty smooth shoot, all things considered, and there's the ever-present sense that outside it's torrential.

At the beginning of the first episode there's warnings of a flood and other hospitals in the area are affected.

Obviously, Holby then gets affected and the water gets into the basement and the consequences are that we lose power, so we're in a constant state of jeopardy.

My character, Joseph, is in theatre with character, Connie, and we're all under stress because we shouldn't be in there and that's where we leave off at the end of the first episode.

Joseph does take a tougher line and on this occasion Connie is the wobbly one because of her personal emotional involvement in it all.

Amanda and I have been working together for some time and we have to shift up those dynamics a little bit and I think it was nice for Amanda to play it a little more frail.

I think Amanda's at her strongest when tough schoolmarm Connie is knocked off her pedestal emotionally. She did a great job and it's kind of cool for my character to finally grow some balls.

We're actors so we always embrace the dramatic - the bigger the better! Holby really excels when there's a major incident that involves the entire cast and unites the staff of the hospital.

Big episodes like the flood are really good because they offer everyone a little more dramatic licence.

, our director of photography, was able to have a lot more fun than he usually does because he has to create a disaster zone - it's basically like the .

You've got these beautiful beams of light across people's eyes but otherwise it's all in darkness and there's flickering lights and, as actors, all we get to see is the shadows, and then they put a little jolt in your knees to make you pretend the lift is broken.

These kinds of episodes are really fun. Personally, I relish it - and I wish we did more of them! But we have to earn them - you can't have them every week in Holby City.

They're also exciting for the audience because the stakes are higher for everyone. The emotional stakes for Connie are high, and then there's Mark () trying to keep everyone together and basically everyone's in danger.

That's what we want - drama! You want instant, cold fear!

It's fun for me because my character's pretty starchy. I mean, I love Joseph dearly but he's quite suit-wearing and nothing's out of place, so it's fun for me to be in scrubs.

Ok, there's not many moments, I admit, but there's a little more chance to play the action hero, running around in and carrying trolleys down the stairs and that kind of stuff.

It's actually quite hard to do. It requires a lot of concentration when you're trying to take a stethoscope out of a bag, or a syringe, or whatever it might be, and you're doing it all on the move and hit our mark and get in the right bit of light and delivering it with the right intensity and not overcooking it.

Paradoxically, even though my character wouldn't normally touch anyone who was even slightly dirty, I inevitably get thrown into the fray to see how my character will react.

There's a real sense of hospital community as everyone's story is interwoven. ' character, Donna, has a story with a missing child and that links into everything else.

Meanwhile, we're throwing everything up in theatre and running out of power, and against the clock and other unforeseen problems. It's dramatic, exciting and involves everybody - it's a real visual treat!

Funnily enough, I think there are about three shots of water in those two episodes - and it's the secondary problems, the electricity and the lack of air-con, and all the other problems.

There are a lot of references to water but fortunately for us, we don't see much. Frankly, actors can often be the last concern filming stories like this and we often get wet and cold in the line of duty but we were spared a soaking this time!

Holby's so much fun - I've done shootouts, delivered babies in lifts, been held up in South Africa, been to Dubai. I've done a lot of running down corridors and sometimes falling down corridors when it goes wrong. More of it for Joseph please!

Luke Roberts plays Dr Joseph Byrne in Holby City

Holby City: Time and Tide Part One is available on iPlayer until Tuesday, 25 May. Part Two is available on iPlayer until Wednesday, 26 May.