UK aid is facing an unprecedented attack from a combination of intense press criticism and rightwing Tory MPs emboldened by the Brexit vote who scent the blood of another of their “pet hates”. The future of the Department for International Development (DfID) as a standalone department and the commitment that the UK will spend 0.7% of gross national income on development is now under serious threat.

It is urgent that those who believe global leadership under successive Labour and Tory governments on aid and development is morally right and in the national interest find their voice before it is too late. A joint campaign involving all political parties, NGOs, faith groups and the public is necessary to ensure that the consensus built over two decades prevails under strident opposition.

In the past year, the government has moved vast amounts of development funding from DfID, with 25% now spent via other departments. The bill currently going through parliament would allow billions to be spent through CDC, the government’s controversial private equity company – an organisation with a track record of using tax havens and supporting middle-income countries rather than the poorest. The fate of the 15% of our aid currently spent through the European Union is uncertain.

There is real concern that diminished transparency could lead to spending on programmes not focused on poverty reduction. This represents a serious threat to DfID’s status as a standalone department within the cabinet.

Theresa May and Phillip Hammond have been unwilling to match David Cameron’s guarantee that the aid budget will be ringfenced, raising questions about our continued commitment to the 0.7% target.

Aid sceptics hope to persuade them that a reversal of aid policy will be popular. Perhaps they forget that Tory support for the 0.7 % target was born out of May’s famous warning that the Tories were the “nasty party” who needed to detoxify their brand. The argument that we cannot afford current levels of aid spending when there are more important priorities at home is spurious. Development leaves 99.3% for other areas of public spending.

A shrinking, interdependent world means good development support has never been more important. Poor governance and poverty breeds extremism and terror, threatening our national security. They are the cause of many people seeking a better life as economic migrants and asylum seekers.

We have learned that conflicts cannot be resolved through military interventions alone. There is a need to combine security, diplomacy and development to end conflict and secure peace. The bringing together of the sustainability and poverty reduction agendas in the new Sustainable Development Goals offers an exciting new opportunity for developed and developing countries alike.

The substantive increase in the number of countries who formerly received aid and are now middle-income countries is good for our future trade. The aid recipients of yesterday are our trading partners of today.

As parents and grandparents, we have a responsibility to prevent children and mothers from dying unnecessarily during childbirth, to allow access to the vaccines which prevent disease and death, to help provide education as a route out of poverty. Should our compassion and sense of duty end at our own border?

I don’t claim that DfID is perfect or that all programmes provide good value for money. Supporters of our aid spending should be the most vociferous in demanding a focus on efficiency and long-term results.

But there must be a balanced scorecard. DfID has earned our country respect around the world for ground-breaking, innovative approaches to development. We have led the way in demanding that global aid spending must be transparent, accountable and focused on results. Committed and highly professional staff work in challenging conditions a long way from home. The shift to a high proportion of programmes in conflict countries means greater risk and less certainty.

Secretary of state Priti Patel should reflect on the fact that some of her department’s biggest problems have occurred as a result of ministerial diktats such as the ideological push to spend vast amounts of money in the private sector without allowing time to develop the necessary skillset.

Brexit means the UK has to rethink its relationship with the rest of the world. Our approach to development should be a key part of our strategic decisions. Far from retreating from our world-leading role, we should define it as a representation of our commitment to social justice and a hard-headed judgment about our national interest.

However, this argument is far from won.

It is time for those of us who believe in development to speak up and speak out.

Ivan Lewis is MP for Bury South, the former DfID minister and the former shadow secretary of state for international development.