Twenty years ago, Gleneagles in Scotland hosted one of the most impactful G8 summits ever held. Tony Blair convened presidents and prime ministers for an agreement that would cut the debts of the poorest countries, increase overseas development assistance and expand key life-changing services including drugs to combat the HIV-AIDS epidemic.

As first minister of Scotland, I was very proud to join the UK PM in welcoming Presidents Bush, Chirac and Putin, prime ministers Koizumi, Berlusconi and Martin and Chancellor Schröder; and to host UN Secretary-General Kofi Annan and many other leaders, including President Thabo Mbeki of South Africa.

The Make Poverty History campaign had climbed on the shoulders of the Jubilee 2000 Drop the Debt campaign, building a mass movement across continents to deliver action by the G8 and the international community.

Two decades later, there is turmoil in the international order that acted so effectively then, with American appeasement of Russian aggression, violent conflict across North Africa, the Middle East and the eastern border of Europe, extreme poverty rising again and the ever-present danger from climate change.

I am proud to see European leaders standing up for Ukraine and I am pleased to see them also rise to this new international challenge and decide to, at last, invest properly in defence and security.  Our prime minister is right to make that commitment.

However, I am not proud that the UK will finance that expansion of our national defence forces by reducing our investment in the lives and opportunities of the poorest people on the planet. And, to do so without warning or a proper transition, will cost lives and create chaos in fragile states that are already too vulnerable to the influence and money of the malign forces we seek to combat.

The cuts announced in UK international aid this week are not just a reduction from 0.5% of GDP to 0.3%. The level of ODA [Overseas Development Aid] domestic expenditure on housing refugees and asylum seekers in the UK means the actual cut is from around 0.35% to 0.15%, taking UK investment in conflict prevention, humanitarian, economic and social development to its lowest level since Margaret Thatcher became prime minister.

Schools will close, medical supplies will stop and economic programs helping the least developed countries stand on their own feet will come to an end. It is bad in principle, but it is also bad strategically.

The focus on Gaza, Sudan and Ukraine does prioritise the most significant humanitarian emergencies of our time. But UK withdrawal from everywhere else, and substantial cuts to multilateral programmes that generate billions more from donors and the private sector, will reduce our influence and soft power.

The world will be less secure and more volatile. And, just weeks after the new government has launched a new soft power council recognising the importance of this work, our strategic positioning across this new world will be diminished.

There are other options for financing the necessary expansion of defence and security and they can still be discussed. The British people are ready for tough, fair decisions. But it is a false choice to say that the UK can only invest in either defence or development.

All serious strategists know that defence, diplomacy and development must go hand in hand if we are to be safe and secure in a world where all can prosper and have a stake in the future. We should do what is right, and the forthcoming spending review does provide an opportunity to revisit these cuts.

During that G8 Summit in Gleneagles 20 years ago, London experienced the horrific bombings that killed and maimed many innocent civilians. The response of the Labour government then was to strengthen our security against that terrorist threat and to increase our investment in international development.

It was not an either/or then and it must not be an either/or now. I hope the government will rethink these decisions and decide that both have to go hand in hand. Then we can engage, defend, influence and invest to be a force for good in this dangerous and uncertain world.

Lord McConnell was Scottish first minister from 2001 until 2007 and is honorary president of the Labour foreign policy group