Sir Stuart Etherington, chief executive of the National Council for Voluntary Organisations, has called on charities to play a part in healing the divisions caused by the referendum, but warned that financial uncertainty could make their work harder.
In a blog on the NCVO website, Etherington said the umbrella body would in the coming days publish a full briefing on the likely consequences of yesterday's vote by the British people to leave the European Union.
But in his initial reaction, laid out in the blog, he said the UK would be facing political and economic unrest for months if not years, and that charities’ advocacy for the people and the causes they work for would "be essential in this climate".
He said: "There is an urgent need to work to restore trust in society. Between the public and institutions, even between members of the public. Every little counts.
"Every negative encounter, every disappointing news story, does its bit to chip away at the finite reserves of trust that people hold. Every positive encounter, everything that serves to reinforce faith, can rebuild those reserves.
"We must all work every day to do what we can to rebuild those reserves."
He said the referendum had left a bitter taste and had exacerbated existing divisions in British society.
He warned that questions of social mobility would come to the fore and there was a clear risk that racial tensions stoked by the campaign would continue.
"We must now play our role in healing these divisions," he said.
"We can and must help people in the communities we work with to understand, respect and cherish each other.
"For so many of you, this is a natural part and parcel of your work, or at least a by-product of it. My message today is that you should consider what more you can do to bring communities together, whether working with other voluntary organisations or with other civic institutions. Outreach and inclusivity in our practices matter now more than ever."
In the wake of the referendum result, the pound fell to its lowest level since 1985, prompting fears of a new economic downturn.
He said further years of economic difficulty "would mean more years of struggling to fulfil our organisations’ complete potential to do good, more years of seeing people struggle in the face of hardship".
He said the sector’s voice would be essential in helping to avoid the worst of the financial predictions, but ultimately the sector was well placed to do so.
"We are entering rough waters – the consolation is that we in the voluntary sector are masters of navigating such seas," he said.
"That expertise will be more important now than ever."