According to the code released by the Institute of Fundraising, which defines best practice in charity direct mail, some charities are enclosing "coins or an expensive umbrella" to 'guilt-trip' the recipient into making a donation.

Megan Pacey, director of policy and campaigns at the Institute of Fundraising, said: "All charity fundraising needs to be thoughtful, relevant, ethical and sensitive and direct mail is no exception.

"Banning enclosures in charity direct mail packs, where the sole reason for their inclusion is to motivate a donation through the inducement of financial guilt, will help to raise standards in fundraisers' use of direct mail and promote its responsible use in the future."

The code allows for the insertion of smaller items, such as pens or a branded bookmark, in recognition that it improves response rates.

Tim Norman, head of logistics at RSPB, agreed with the new code: "Charities have, as a whole, moved on from these practices. We don't send out any expensive incentives and never have done.

"Our free gifts have been items like pens which fulfil a use and are made from recycled materials. I think there is both a moral and environmental reason not to guilt people with expensive gifts – or gifts that are perceived to be expensive."