Former EastEnders star Anita Dobson tells us about her killer guest role in Casualty (BBC1, Saturday) as a chemist with murder on her mind…

It sounds like you’ve got an exciting storyline in this week’s Casualty – what can you tell us about it?
“Myself and Andrew Sachs play a Jewish couple who run a chemists, which is being plagued by a local drug addict. The youth, Craig, has been constantly threatening Rachel and Mendel with demands for methadone for 18 months and it gets so bad Mendel says he can’t take it any more.”

What happens when Mendel stands up to Craig?
“The boy smashes up the shop, a scuffle ensues, and Craig stabs Mendel with a piece of metal!”

Where’s Rachel when this is happening?
“While the shop is being smashed up Rachel goes into the back to get the methadone, but while she’s there she mixes it with something else.”

Is there a sense that this is an act of desperation?
“Yes, she’s petrified. She’s frightened her husband will be killed and she wants it to stop. It’s a knee-jerk reaction to what’s going on in the shop.”

What are the consequences of her actions?
“Mendel has a terrible time when they get him to hospital – his heart stops for a while and he goes into a coma. And while this is going on Rachel sees Craig in there with his pregnant girlfriend – who has also taken the methadone. The ED staff don’t know how to treat them because they don’t know what it’s been mixed with.”

This must present Rachel with a terrible dilemma?
“Yes, as Craig and his girlfriend get sicker and sicker Rachel has to decide whether to confess what’s happened and risk imprisonment – or keep quiet and possibly watch them die. And while this is happening she’s also wondering if her husband is about to die.”

So your usual cheery Casualty storyline!
“Yes! It was great fun to do, Andrew and I really enjoyed ourselves. I love doing Casualty, as it’s such a happy, tight-knit group. I’ve had a couple of Casualty appearances and every time I find it’s a well-run ship and I have a fantastic time.”

You played a psychic the last time you appeared on the show…
“Yes, Cora the little, old psychic! Michael French who plays Nick Jordan said, of all the characters I’ve played, she was his favourite. I’m having a run on little old ladies at the moment.”

Do you feel typecast?
“I think I’m slowly moving into the autumn of my life. But you know what, bring it on! It’s quite relaxing to play parts where you don’t have to worry if your hair is in the right place, your makeup’s not smudged and you haven’t creased your blouse!”

What do you think made your EastEnders’ character, Angie Watts, so memorable?
“She was a real survivor. You’d knock her down and she’d fall flat on her face – a crying, drunken wreck. But she’d get herself up the next morning looking a million dollars and be in the Queen Vic with a big smile on her face. She could look really glamorous and absolutely dreadful! And there was a fearless quality in her – you’d see her eyes flicker around, while her brain was thinking ‘How do I get out of this one?'”