The commission's advice, of special relevance during the current election campaign, was revised last September after charities requested election 'do's and don'ts', and has been presented to the sector as a reminder about maintaining independence.
Caroline Cooke, head of regulatory policy at the Charity Commission, said a charity's entire funds may now be legitimately directed into one campaign, but "there must be a clear rationale for the campaign, with a specific beginning and end point".
The campaign may have a political end, but the charity can't back any political party.
The commission hasn't set an upper time limit for a campaign, because it depends on the particular charity, said Cooke. She did, however, highlight clause 24, which warns that questions will be asked if the activity continues over a prolonged period. It says: "Where political activities dominate the activities of the charity, an issue will arise as to whether the charity trustees are acting outside their trusts."
The thrust of the Charity Commission's advice is how to remain an independent voice. It warns charities not to help any party with its campaign, financially or otherwise, and to keep their positions separate from those of political parties.
NCVO has also issued practical election advice on promoting causes, and asks charities to push its own manifesto on ensuring the next government's voluntary and community sector policy is "about more than just public services".
- See Election '05, page 9.
Charities that produce bulky election manifestoes are wasting their time, said Labour MP Tom Levitt, chairman of the all-party parliamentary group on charities and the voluntary sector.
With the General Election just three weeks away, charities are bombarding parliamentary candidates with demands.
But Levitt advised them to be realistic about what they could achieve.
"Not many sincere and genuinely informed MPs are going to be changing their views about anything at this stage," he said. "And not many voters will genuinely be waiting for their favourite charity to tell them how to vote, either."
He said organisations would enhance their chances of getting noticed by lobbying through umbrella organisations such as the NCVO.
But the golden rule was to keep their letters down to one sheet of A4 paper.