Fewer people are giving to charity, in what researchers say is a worrying trend at a time when trust in charities appears to be falling.

The proportion of the UK public who gave money direct to charity in 2018 dropped to 57%, compared with 60% the previous year and 61% in 2016. Numbers giving money or sponsoring someone fell to 65%, compared with 67% in 2017 and 69% the year before.

The Charities Aid Foundation (CAF), which produces the estimates based on online surveys, said there had been a clear downward trend over the three years, a period during which the charity sector was rocked by scandals.

Forty-eight per cent of people believe charities are trustworthy, according to CAF’s figures. The proportion explicitly disagreeing has risen to 21%, with the remainder neither agreeing or disagreeing. Among those aged 65 or over, traditionally the most regular supporters of charities, 46% agree and 23% disagree.

Susan Pinkney, CAF’s head of research, said: “If people lack trust, that means they worry that their hard-earned money is not being well spent when donated to charities. This is a challenge that the entire charity sector needs to tackle head-on and find ways to inspire people to give and demonstrate to them that their money is making a difference.”

The findings will be unwelcome for charity leaders, who have been seeking to move on from debate over trust and confidence sparked by the Kids Company affair, controversy over fundraising techniques, and last year’s revelations of sexual abuse and other safeguarding scandals at aid charities.

Last month, sector leaders were privately angered when the Charity Commission regulator concluded that the collapse of the garden bridge project across the Thames in London had been another “failure for charity”.

The National Council for Voluntary Organisations (NCVO), the leading umbrella body for charities, believes the CAF figures say less about trust and more about deliberate changes in fundraising in 2018 in response to the earlier controversies and GDPR data protection rules that took effect last May.

Significantly, the CAF survey found fewer people had been approached to make a donation in the street or on the doorstep last year, or received direct mail requests. The overall amount raised from household donations remained steady, however, at £10.1bn.

Sir Stuart Etherington, the NCVO’s chief executive, said: “Fewer people giving larger sums reflects a year in which many charities were scaling back recruitment of new donors and focusing instead on cultivating their relationships with existing supporters. This is the result of a positive change in charities’ fundraising strategies away from some of the marketing approaches of the past.”

While acknowledging supporters did appear to be giving more, Pinkney said: “With three years’ worth of data, we can now see a clear trend in people’s charitable giving and it is headed in a worrying direction.”

The CAF survey, based on more than 13,000 interviews last year, also asked people if they had taken part in any “social action”, such as joining a rally or protest, buying an ethical product or signing a petition.

The proportion of people saying they had done so in the previous four weeks fell in 2018 for the second year running, to 64%, compared to a peak of 68% in 2016. But CAF said early results for 2019 showed an upturn, hitting 69% in March, probably reflecting the numbers who signed one of the mass petitions on Brexit.

The reported rate of volunteering for charities remained stable in 2018, with 16% saying they had done so in the previous 12 months, as did the rate of goods donated to charity shops, at 56%.