Government attempts to increase giving will struggle to succeed and might lead only to a "reshuffling of existing giving", according to academics at Bristol University.
The Office for Civil Society published a giving green paper a year ago to "build a stronger culture of giving".
Writing in the latest edition of the journal Voluntary Sector Review, professor Sarah Smith and researcher Michael Sanders conclude that "achieving a step change is likely to be a challenge".
They say changes in tax relief appeared to have "little effect" and there is "little evidence to suggest US-style tax rebates would have a large positive effect on giving".
The pair highlight evidence that shows individual charities could benefit from certain behavioural techniques, such as offering people the chance to give in the future rather than now, or asking for specific sums.
But Smith and Sanders say studies have demonstrated "specific ‘nudges’ or interventions can increase giving for an individual charity" but not for total donations.
"The real test for any proposed policy is not just whether it is likely to be taken up and whether it can increase giving in a specific case, but whether it has a positive effect on either overall participation or amounts," they wrote.
"Only innovations that can succeed in increasing the total number of donors and/or the total amount donated will really make a difference to the overall level of giving."