A lack of military support for Ukraine could eventually lead to “Russian boots on the ground” in NATO territory, former Ukrainian president Petro Poroshenko has warned.

Mr Poroshenko told Sky News that Russia has 12 to 15 times more artillery shells than Ukraine can “give them in return”.

He welcomed a Czech-led initiative to source 1 million shells for Kyiv from non-European countries but said more help was needed – and military support needed to be accelerated.

It’s “dangerous” that a $95bn US security bill predominantly containing military aid for Ukraine remains stalled in Congress, Mr Poroshenko said.

“There is just a very high risk that Russia can have limited success on a limited period of time. With that situation, we need to do our best to accelerate that and to make a decision of the hour,” he said.

He went on to say: “I just want all British people, all Europeans, to understand that less weapons [means] more chance that the boots of the Russian soldiers would be on the soil of the NATO member states.”

Mr Poroshenko warned that a Ukrainian defeat would be a “defeat of Europe” and the “whole free democratic world”.