Over the past few weeks, the newspaper has been investigating a tip-off that an unnamed charity had made a "substantial payment" to a "high-profile model".
But charities have rubbished the idea that they would pay anything more than expenses to a celebrity supporter who was helping to publicise a campaign.
Leigh Daynes, head of media and public affairs at the British Red Cross, says: "They are volunteers who have given their time for free to raise awareness of our cause, and they help us reach a mass audience."
Daynes says the charity would cover a celebrity's stay only in modest accommodation, and not in a five-star hotel. It would pay for them to travel only in economy class if it was inviting them to one of its projects abroad, he adds.
Daynes admits that the charity might pay a celebrity to provide entertainment at a large corporate event, such as a ball, although he stresses that the sponsor would usually cover the costs.
"I don't think it's unreasonable for a celebrity to be paid in those circumstances," he adds. "They have to earn a living too."
Maria Pedro, celebrity officer at the NSPCC, agrees. "Entertainment at a ball is critical," she says. "We would hire celebrities to provide it in the same way that we would hire caterers."
However, the idea of even covering the cost of an economy class airline ticket for a celebrity who earns more in a month than most earn in a year might raise eyebrows. Research by the ImpACT coalition, which aims to improve trust and accountability in charities, shows that only 9 per cent of those surveyed feel it is acceptable for charities to invest in fundraising.
Given such figures, it's easy to see how a national paper might present the facts in a less than positive way.
The investigation raises the issue of how the sector should deal with such media enquiries. The NSPCC carried out a formal evaluation of its Talk 'Til It Stops campaign last October, which was backed by celebrities including the boxer Amir Khan. The evaluation - by the media analyst Metrica - showed that 404 press articles were generated and that 75 per cent of those classed as 'strongly favourable' mentioned a celebrity supporter.
For the British Red Cross, however, limited resources mean that a formal evaluation can't always take place. Daynes says: "Demonstrating our return on investment can be a costly process, but this should not preclude our absolute obligation to be accountable."