Late last night I was at the Foreign and Commonwealth Office to attend a crucial gathering of Ambassadors and embassy officials from dozens of different nations.
A few short weeks ago, the United Nations agreed to adopt the world's first international arms trade treaty.
This treaty has the potential to stem the flow of weapons to conflicts; conflicts where thousands of people are killed, injured, raped, and forced to flee from their homes. And last night's event marked the culmination of decades of hard work from Amnesty International, a wide coalition of NGOs and politicians of all colours. But the treaty still has some hurdles to clear.
On 2 April, 155 nations agreed to adopt the treaty, but now those nations need to turn their words into action.
On 3 June, the treaty will be opened up to nations to sign. To come into force 50 of those signatures need to ratify it. And that's why last night's meeting was so important.
The gains achieved in the Arms Trade Treaty will only be realised if the treaty is rapidly and effectively implemented and robustly enforced. It is now up to the likes of Amnesty to build on the momentum we created in the run up to the vote in April to ensure that this happens.
To the many ambassadors and representatives of Foreign Ministries I met last night, I had one clear message: Make sure your government attends the signing ceremony, sign up and encourage others to follow suit.
Our target is that within 24 hours the required number of signatures is not just reached but far surpassed. That would send out a clear message to the three nations that voted against the treaty - North Korea, Syria and Iran - that the rest of the world is serious at regulating the arms trade. By the end of the evening several nations had pledged to sign on 3 June.
I have seen first-hand how important the treaty is. Last year I went to Afghanistan. I remember being in Kabul and how it was commonplace to see men with guns strung across their shoulders.
The level of insecurity is so great, it's almost tangible. Hardly anyone goes out at night there. I spoke to one woman human rights defender who told me how they needed to get control over the way weapons are being used in the country. Arms have poured into Afghanistan from almost every weapons-supplying country in the world and they have ultimately changed the way people live.
But it is not just in Afghanistan where the treaty could make a huge difference.
Every minute of every day at least one person dies from armed violence and conflict.
Add to that the millions of men, women and children who are caught up in the effects of armed conflict through injuries, through schools, homes and hospitals being destroyed or through people being forced to flee their homes.
The fundamental purpose of an Arms Trade Treaty still remains. It must reduce the human suffering. It must protect human rights and uphold international law by categorically adhering to the so-called 'Golden Rule' - a rule that no arms should be supplied to anyone where there is a clear risk that those weapons would be used to facilitate atrocities.
The Arms Trade Treaty is needed to help save lives and to help protect people from armed violence and armed conflict.
An Arms Trade Treaty is needed to help reduce human rights violations and give people a better chance of escaping poverty.
It has been a long journey. The idea for the treaty was mooted by an Amnesty International representative some 20 years ago. And on a personal level, I have been campaigning for 10 years to reach this moment.
One of my greatest memories over that time is the Control Arms Mass Lobby of Parliament in 2006.
I remember standing outside the Houses of Parliament with hundreds of Amnesty, Oxfam and IANSA supporters waiting to enter to meet with our MPs. We wanted MPs to urge the Prime Minister at the time, Tony Blair, to commit to securing agreement to start negotiations for an international Arms Trade Treaty when world leaders met later that year at the United Nations. It was also on this day that David Cameron - as leader of the Opposition - also voiced his party's support for an Arms Trade Treaty. It was breath-taking to see such cross-party support for this campaign.
That memory was only eclipsed by the joy of seeing the United Nations finally adopt the treaty earlier this year, some seven years later.
And now we are on the verge of seeing it come into force. We campaigned for this treaty to save lives and regulate this deadly trade. Last night marked another step on the path to making it happen.