Joint authors Paul Streets and Dan Corry, the chief executives of the two charities, use the paper to call on foundations and trusts to "do a lot better" in using their influence beyond making grants.
The "provocation paper", called Grant-makers Must Learn New Tricks and published today, argues that foundations should "exploit the potential of their knowledge, expertise, data, networks, convening power, and human energy and talent" to effect social change.
By worrying about the power they have in the sector, some wealthy funders are guilty of inaction in terms of making non-financial support available to grantees, the paper says, and are not ambitious to become "agents of change rather than just funders of it".
It also recommends that foundations explore additional ways of supporting charities that complement funding, including offering help from specialist staff and making office space available to grantees.
The publication notes that at £6.5bn the total value of grants made to civil society by independent foundations each year is now greater than grants made by government.
The paper is released alongside two other research reports by NPC and the Lloyds Bank Foundation, which investigate funding practices around the world.
The papers highlight work carried out in Greece, where a foundation has developed peer-support networks for providing training and an initiative in Nicaragua where foundation staff run sessions for grass-roots groups.
Corry said: "Grant makers matter to a healthy voluntary sector, and how they spend their money matters too. While many strive, they can do a lot better.
"In particular, if you want to create positive, lasting social change, funders must not shy away from supporting campaigns that charities do to promote policy, behaviour and system change. And while it is fine to fund good programmes and interventions, you also have to fund the things that make a charity effective and sustainable. Funders know all this makes sense; we have demonstrated different ways that they can approach this."
Streets said: "The climate for charities is tough and the demand high. As they constantly evolve to ensure their survival, it’s our job as grant-makers to change too. We need to be more vocal on behalf of the causes, charities and communities we fund and broaden our support for them to ensure they can thrive for the long term.
"The global insights from these reports will be key for us in shaping and improving our own offer and, we hope, raising the bar for other funders across the UK."