Ukraine repeatedly asked to buy weapons from Britain for seven years but was refused by three successive prime ministers, according to reports.
The former defence secretary Michael Fallon has accused successive governments of being reluctant to support Kyiv in the aftermath of Vladimir Putin's annexing of Crimea in 2014.
When serving under former prime minister David Cameron, Mr Fallon said he was told to turn down requests for assistance in upgrading Ukraine's defences despite the Ministry of Defence wanting “to do more”.
“We were stymied and we were blocked in cabinet from sending the Ukrainians the arms they needed,” Mr Fallon told the Sunday Times.
“Some in the cabinet felt extremely strongly that we should do nothing to further provoke Russia.
“I felt that was absurd. The Russians didn't need any provoking. They were already there, sending people across the border.”
Liam Fox, another defence secretary under Mr Cameron and who spoke out against the failure to arm Ukraine as a backbench MP in 2015, told the Sunday Times: “It was very clear what [Putin’s] pattern of behaviour was and it was very clear that Ukraine would be next.
“There was no logic whatsoever in saying, ‘Well, we can’t give the Ukrainians the ability to defend themselves in case of provoking Putin’.”
The revelations come as Ukraine’s president Volodymyr Zelensky thanked Boris Johnson for currently training members of his military on UK soil.
Mr Johnson spoke to Mr Zelensky on Saturday afternoon for an update on Kyiv's conflict with Russia.
A No 10 spokesperson said: “President Zelensky thanked the prime minister for the training of Ukrainian military personnel currently taking place in the UK.”
In a press conference in Kyiv on Saturday, Mr Zelensky declared that he was "satisfied" with the level of military supporting coming from the UK.
He told reporters: "We want more than we're being given, but we're satisfied.
"We cannot refuse or reject anything during the war from the biggest military aid, which is coming from the United States and the United Kingdom.
"There are many other friends in Europe, but I'm talking about volumes of help and I'm grateful for it."
Russia has intensified fighting in the east as Saturday saw several civilians killed in Mariupol and Kharkiv while remaining civilians and Ukrainian troops in Mariupol hold out against shelling on the Azovtal steel plant.
A government spokesman said the UK has been at the forefront of the international response to Mr Putin’s “special military operation” and has provided “unprecedented financial, military and diplomatic support to Ukraine.
