LORRAINE McIntosh isn’t usually lost for words.

We’ve all seen her perform effortlessly the long soliloquies required in stage plays such as Men Should Weep.

Or deliver cutting, sharp lines in the likes of Greg Hemphill’s TV horror-comedy Long Night At Blackstone.

And we’ve heard her speak eloquently on Radio Four chat shows such as My Life In Five Songs or in interviews featuring her role in Deacon Blue.

But in conversation at the Tron Theatre bar, where she’s in rehearsals for The Mistress Contract, the McIntosh mouth isn’t processing thought at the normal rate.

Why? Well here’s a clue. The actress and Deacon Blue star is set to star alongside Cal Macaninch in Abi Morgan’s The Mistress Contract.

It tells the story, based on a real life tale, of a couple who call themselves He and She, who first met at university and then lost touch. When they met again twenty years later they began an affair .

But it was an affair with a contract attached. She – a highly educated, intelligent woman with a history of involvement in the feminist movement – asked her wealthy lover to sign the document that outlined their unconventional lifestyle: The Mistress Contract.

The material for the play emerged from the recorded conversations made during their 30 year-relationship, and they talk of how He has paid for her home but in turn She provides “mistress services,” ie, sex and support.

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Yet, the premise of Morgan’s play (whose credits include The Iron Lady starring Meryl Streep and BBC2’s The Hour) however throws up a range of tricksy questions for the modern day feminist.

Can a mistress indeed by a feminist? Is a woman who forms a relationship with a married man subjugating herself to that man by accepting the secondary relationship role?

Why does a woman effectively surrender the hope of a relationship with someone single to become the “other woman”?

Is this contract a betrayal of all that she and the women of her generation had fought for? Or was it brave, honest, and radical?

McIntosh smiles as she deliberates over her answers. “I don’t know,” she says after a few seconds. “I think the term ‘Mistress’ is very loaded.”

What does that mean, Lorraine? Can you say The Mistress has made the right choices?

“Well, it’s a very complex issue. I suppose ‘I’m not sure’ is the answer I have to give. I do feel though that when deception is involved, well, that’s not good for any relationship.”

There is the question of how society judges “the other woman”. The watching world hasn’t been too kind, for example, to famous second choices, from Anne Boleyn to Monica Lewinsky, to Camilla, Duchess of Cornwall. “What I do find interesting is that it’s always the woman under discussion when we talk about affairs,” says the actress. “We don’t seem to talk about the man.”

That’s valid; the single man who has the affair with the married woman isn’t labelled with what is seen to be a pejorative term.

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McIntosh agrees; “I don’t think there is a level playing field. And in the play what is revealed is that the woman is broke. She is also trying to make sense of her life.

“If you look at the stats in Scotland today 75 per cent of those in poverty wages are women. There is a huge inequality. Women suffer in lots of ways. So in this situation I can feel sympathy with the woman’s desire to survive. And we learn, she has been in a relationship before where all she’s been left with are “a couch and cutlery.”

There are other issues raised by the premise of a play. Sometimes a mistress feels she is helping her lover’s marriage along, by providing an alternative. Sometimes mistresses have no desire to be in love, or to be looking for a full-time commitment. They can often separate sex and love. And a married man ticks their boxes.

But is She letting down all the women of the world by surrendering to He and becoming an Occasional?

“I think a play like this certainly causes us to think about that argument,” says McIntosh, who married Deacon Blue frontman Ricky Ross in 1990.

“I like the fact it talks about a vulnerable woman who feels she gains control by setting up this contract. She says if you give me certain things I will offer you companionship and sex. But this contract raises all sorts of questions; they ask if sex is simply a transaction, can it be monetised?”

McIntosh doesn’t have the answers. “But we’re having a conversation about it, which is great.”

McIntosh is aware the subject is a minefield. She’s acutely aware that comments can be taken out of context on social media and the result is vilification.

Did she learn this from the example of taking a stance on Scottish independence? “Yes, I did, And in fact Ricky, because of his BBC radio work effectively talked himself out of a job for six months because of this. And it’s difficult when you read about Deacon Blue fans saying their concert tickets are going in the bin.

“But there are certain times in your life when you have to nail your colours to the mast.”

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The key issues – a nation’s future, indeed the future of the planet – command the McIntosh voice to speak out. “We have to talk about climate change,” she maintains.

“That’s why I think the protests have to be supported, as do the children who are part of the movement. Yet, we also have to respect each other. We have to listen to opposing views.”

The Mistress Contract will certainly offer up thought for debate?

“Lots of it,” she says with a knowing grin.

The Mistress Contract, The Tron Theatre, May 1 – 11.