The Czech President, Petr Pavel, made an eye-catching suggestion this week: Ukraine could join NATO while it’s still partially occupied by Russia.

So why is the proposal surprising and could it work? We’ve spoken to one of the UK’s leading security experts, Professor Michael Clarke, to find out.

What is NATO?

The North Atlantic Treaty Organization (NATO) is an alliance of European and North American countries, including the US and UK.

Its key principle is shared defence – so if one member is attacked, the other nations must provide support under Article 5 of the founding treaty.

Why isn’t Ukraine part of NATO?

Ukraine has been slowly edging towards NATO membership in recent decades. In 2008, the alliance agreed that “Ukraine will become a member”. And from 2017, Kyiv began passing laws distancing itself from Russia and moving closer to Western allies.

But when Moscow launched its full-scale invasion in 2022, this progress was cast into doubt. NATO states provided financial and military support, but stopped short of admitting Ukraine into the bloc.

The thinking goes that if Ukraine becomes part of NATO, the other member states will be obliged to defend it against Russian aggression. That could mean direct warfare between nuclear powers – NATO members the US, UK and France versus Russia – which no one wants.

What did the Czech President say about Ukraine joining NATO?

That’s why the Czech President’s comments this week were so surprising. He told the Czech news site Novinky that “full restoration of control over the entire territory [of Ukraine] is not a necessary prerequisite” for NATO membership. He said the alliance could accept a “temporary” “administrative border” between land under Kyiv’s control and the Ukrainian territory currently under Russian occupation.

Could Ukraine join NATO while still under partial Russian occupation?

We put this to Professor Michael Clarke, a former director of the Royal United Services Institute and specialist adviser to the Joint National Committee on Security Strategy.

He told FactCheck: “It would require a change in the principles of NATO membership that no one joins the alliance with an existing conflict over its legal borders”. The President’s idea “could be politically feasible”, he said, but “would be a big departure for NATO”.

And, he said, it could have a major downside for Kyiv. President Pavel’s suggestion would mean tacitly accepting, albeit temporarily, that Russia is in control of parts of Ukraine’s territory – as those parts would not be joining the alliance. Professor Clarke says this “would be used by Russia as evidence that it proves the territories [currently under Russian occupation] not included are not a sovereign part of Ukraine” and “would certainly diminish” Kyiv’s legal claim to the land.

Professor Clarke told us that in his view, Kyiv joining the bloc “would not bring peace now” but that “NATO membership for Ukraine at some point in the future is the only way the ‘armed peace’ that may result from this war can be stabilised for Europe.”