Heavy rain and flooded grounds have forced this weekend's show at Hoghton Tower, near Preston, to be axed for "health and safety" reasons.
The gig by the 2002 Pop Idol winner was part of an annual event to raise funds for Preston's St Catherine's Hospice.
Thousands of people were expected at the weekend-long Symphony at the Tower fundraiser for the charity.
A second classical concert planned as part of the event has also been scrapped and a third, by Joe Bonamassa, has been moved to Preston Guild Hall on Saturday.
Stephen Greenhalgh, chief executive of St Catherine's Hospice, said: "Having thoroughly examined the saturated ground conditions and every option for our flagship event it was with great disappointment that we could not go ahead at Hoghton Tower on grounds of safety."
A spokesman for the promoter said: "The torrential rain this week has made the Hoghton Tower arena site unsafe and, after taking health and safety advice, we have regrettably taken the decision to cancel."
Customers who booked tickets online, or by telephone, will receive an automatic refund within 14 days, organisers said.
A hospice has said it is "greatly disappointed" a fundraising concert by pop star Will Young has been cancelled.