The singer, who wowed the judges on last night's show with her version of 'This Woman's Work', started working with the producer last year after he spotted her on YouTube.
"I did some songwriting with him and he said he thought I had potential and he wanted to see how I would handle different circumstances in the studio," she told The Mail On Sunday.
Asked why she hadn't been signed by the producer, Murphy said: "He said my weight might affect me being an artist. He never said it in a horrible way - he just said it was best for me as an artist.
"Adele has been a massive inspiration because she is a bigger girl who has done well. I don't think anyone pays attention to her weight because she is so talented.
"When I was younger I got some stick but now, because I am so passionate about singing, no one ever mentions it. I am comfortable with where I am and I am going to concentrate on my singing, not the weight."
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Watch Hope Murphy perform 'This Woman's Work' on Britain's Got Talent below: