The government has dropped the principle that consultations should automatically last 12 weeks, the Cabinet Office has announced.
A written ministerial statement from the policy minister, Oliver Letwin, said the government wanted to make consultations more proportionate.
Letwin said the new guidance, which will come into effect in September, would replace the code of practice on consultation published in 2008.
"This means that departments will follow a range of timescales rather than defaulting to a 12-week period, particularly where extensive engagement has occurred before," he said. "Policymakers will need to give more thought to how we consult with people. The aim is to replace potentially unproductive process with real engagement with those who are affected."
The Compact, the agreement that sets out how government and voluntary sector organisations should behave towards each other, says 12-week consultations should take place where it is appropriate, to allow "meaningful engagement".
The ministerial statement said: "The principles of the Compact between government and the voluntary and community sector will continue to be respected."
Neil Cleeveley, director of policy and communications at the local umbrella body Navca, said that changing the length of the consultation period would not prevent effective work being done, but changes should not dilute the effect of inter-working.
"Let’s remember why we have consultation," he said. "It isn’t done as a favour to the voluntary sector; it’s done because talking with service users and organisations delivering services leads to better services and more efficient public spending.
"The important thing is that consultation is genuine. Decision-makers need to be sincere in their efforts to seek views and they must listen and act on responses. If it can be done well in less than 12 weeks, fine – have a shorter consultation period."
But he said the changes "should not be an excuse for dodging the principles of the Compact".
"The priority should be to ensure meaningful consultation that responds to local people’s needs," he said.
Tom Elkins, manager at Compact Voice, which represents the voluntary sector on the Compact, said the statement provided "helpful clarity" about how government departments would consult.
"As well as recognising the importance of the Compact, the minister’s guidance also strengthens commitment to proportionate and realistic timeframes to allow stakeholders to respond," he said.
"We expect that this should be in line with the principles of the Compact, and that consultations should also be accompanied by clear explanations and descriptions of how they have been made genuinely meaningful, particularly in those instances when the recommended 12 weeks has not been followed."