Roopi Woodall admitted she went to buy two tickets thinking it was an immersive theatre experience - but after finding out it was for the show, thought "Oh well, in for a penny".
The brave 40-year-old said she did not expect to put herself through the rigorous challenges to test if they had what it takes to be a spy, but after being selected from 2,000 applicants, she could not turn it down.
She told getwestlondon: "I just tried to look at it as a challenge.
"When am I going to be able to test myself like this ever again? I wondered if I still had it in me to be tough."
After going through various testing tasks, including having the ability to lie, the Southall born candidate said she was totally absorbed in the experience.
She laughed at being called "a brilliant liar", before adding in real life, she chooses "not to betray people's trust".
The long term west London resident said despite what it looked like, the show was not fun and was the most "gruelling thing [she's] ever been through".
Yet Roopi managed not to drop out, which she said she almost considered when things got difficult.
"When I first graduated, I looked at spy work but that was amongst a lot of things," she said.
"Besides, I realised I was too chatty to be a spy, there's no way I could keep a secret.
"I really wanted to do it once I found out what it was I'd applied for, but just without being on TV."
Now working in marketing, Roopi was apprehensive about appearing on television, fearful of getting online abuse and being trolled.
Crossing the hurdles, she told getwestlondon the experience taught her a lot about herself after keeping a diary of her days during the filming.
"I learned that I am just as tough as I was, if not tougher and I'm proud of how I did in this process.
"It's a once in a lifetime opportunity - and it's good TV!"
Channel 4 spies is on every Thursday at 9pm.
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