Harding - who is said to have flown to Ibiza where Crane was working in a bid to save their romance - apparently ended their relationship after a series of rows.
According to The Sun, the 29-year old has "been in floods of tears" since parting ways with Crane and has refused to answer her mobile phone for three days.
A source told the newspaper: "Sarah and Tom had a huge bust-up and told each other the wedding is off. Although they've always managed to patch things up in the past, it's worse than anything they've gone through before."
"They've been fighting like cat and dog. Their relationship has been strained because he's been in Ibiza for the summer and Sarah was working here. They've always had a volatile relationship but this time it's far worse."
The insider continued: "If they do get married, they both need to start living their lives differently — and that's not going to happen any time soon."
"It's a shame as they do really love each other but pals can't see how there can be a way back from this."
Crane proposed to The Loving Kind singer on New Year's Eve in the Maldives, with reports suggesting that Harding was "buzzing" over their pending nuptials.
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