When the Soviet Union collapsed, Britain, Russia and the United States made a solemn agreement with Ukraine. In exchange for giving up its inheritance of the third largest nuclear arsenal in the world, Ukraine’s security was to be guaranteed and its independence would be respected.

Ukraine has kept its end of the deal. Vladimir Putin has not. Russia has annexed Crimea, provided support for separatist conflict in Donbas and massed 100,000 troops on Ukraine’s border. In doing so, it has committed repeated acts of aggression, provocation and interference.

It is not enough for Western politicians to talk about the importance of our values. When they are tested, we must support our allies. Not only does Labour understand the threat posed by Putin’s Russia, we stand resolute in our support of Ukrainian sovereignty, independence, and territorial integrity. I made that clear to the Ukrainian ambassador to the UK this week.

The situation on the Ukrainian border is an attempt by Putin to re-establish Russian force as a means of dominance over parts of Europe. And it is a direct threat to the anti-imperialist principle that sovereign nations are free to choose their own allies and their own way of life. 

That is why it is crucial that parties in Westminster are united in opposing Russian aggression. I’ve been critical of the chaos at the heart of the UK Government. But I must commend the work of the Secretary of State for Defence, Ben Wallace, on this matter. He has worked hard to bring people together, written with moral clarity on the nature of Russian aggression and ensured that the UK continues to support Ukraine’s ability to defend itself through military aid. 

These bilateral measures are important but if we are serious about repelling the Russian threat we will need a more united approach on an international level. This is where I believe the Government must step up and lead. Divisions within Nato have emboldened Putin. For too long the implicit message to Moscow has been that Putin can do what he likes and the West will do little to retaliate. 

We must continue to explore diplomatic routes to avoid conflict. But Russian demands that Ukraine give up its desires to join Nato and the EU should not be entertained. Nobody envisages British and allied troops being dragged into war. But we need to work with allies to use our collective resources, including sanctions, to show Russia the actions it takes will have consequences. 

For Britain and our allies this will mean taking tough decisions. Europe’s over-reliance on Russian energy supplies must be addressed. And here in Britain there has been a failure to rid our economic and political systems of the money used to fund and support the Putin regime. We cannot go on being the world’s laundromat for illicit finance. 

First, we must lift the veil on the true nature of ownership of property and other assets in the UK. That requires a registration of overseas entities bill. Second, we need reform of Companies House. There is no reason for ownership to be hidden behind layer after layer of shell companies whose only purpose is to obscure the facts from public view. 

Third, the Government must act on the recommendations in the intelligence and security committee’s Russia report. That means dealing with shortcomings in the unexplained wealth order regime and for a register of members of the Lords or Commons who serve on the boards of overseas companies.

Fourth, we must ensure that the elections bill going through parliament requires political donations to be transparent, and to come from money generated in a legitimate fashion. 

To reinforce all this, Labour has announced the formation of an illicit finance taskforce with the aim of making the UK the most difficult place to launder money.

Labour is proud of our internationalism. We are proud of our role in creating Nato. To continue to protect our values and our security we must be steadfast in our opposition to Russian aggression. We must stand with our Ukrainian allies and defend their right to independence. And we must get our own house in order by playing our part in ridding the West of its dependence on the loot of Russian kleptocracy.

Keir Starmer is Leader of the Labour Party