Britain has been embattled Ukraine's most visible benefactor

ITV News Senior International Correspondent John Irvine reports on the latest developments in Ukraine as Boris Johnson issued a warning to Moscow

The RAF’s C-17 Globemaster transport planes have flown several sorties into Kyiv, bringing a total of 2000 of Britain’s very latest shoulder-fired anti-tank missiles.

They were the same aircraft that had a starring role in the retreat from Kabul last August.

Why, you might wonder, has Britain been doing its bit for the defence of Ukraine?

It’s because 28 years ago we promised.

In 1994, the US, UK and Russia were signatories to the Budapest Memorandum which committed the countries “to respect the independence and sovereignty and the existing borders of Ukraine.”

The commitment was backed up by security assurances.

In return the Ukrainians agreed to get rid of the their huge nuclear arsenal. They had 1,900 strategic nuclear warheads at the time, a hangover from Soviet times.

The other nuclear countries at the time, France and China, did their own deals with Ukraine and gave weaker assurances.

Ukraine became the poster-child for nuclear disarmament.

In 2014 Russia drove a coach and horses and many tanks through the memorandum, arguing that the Maidan revolution – which saw the overthrow of their puppet president in Ukraine – created a new state, which wasn’t the one they had done the deal with.

But the United States and the United Kingdom appear to be trying to honour their 1994 commitments.

But to what lengths will they go?  And if Ukraine is taken over by Russia, how will other countries be persuaded to give up their nukes or their quest for them?