It's true that Ukraine summarized a proposed peace deal between itself and Russia in a two-page document it called the Istanbul Communiqué, named after the city where it was drafted, and because Turkey acted as intermediary.
This deal fell through, but it's a bit more complicated than just the US and UK scuttling it. In the first place, according to the NYT, there was uncertainty about whether Russia's delegation was acting in good faith, with some Ukrainian negotiators saying they believed the negotiations were a bluff on Mr. Putin’s part, while others described them as serious. Further, there were big problems with the revised version of the deal that Russia came back to the table with a month after the first version of the deal. An analysis by PILPG (Public International Law Policy Group) mentions a number of flaws in the deal, perhaps the most egregious being the article that stated that if Ukraine were attacked again, the "guarantor states" (potentially including Great Britain, China, Russia, the United States, and France) would come to Ukraine's defense. There was a problem, though:
The draft treaty also failed to resolve whether a unanimous consensus among all Guarantor States, including Russia, would be required to activate any assistance. If adopted in a final peace agreement, this provision would replicate the dysfunctional decision-making model of the United Nations Security Council’s veto system. It is unthinkable to design security guarantees that give veto power to the very aggressor responsible for initiating the war.
The US and UK did continue to fund Ukraine during this period (which could implicitly be read as the desire to prolong it), and the US proposed a deal that both Ukraine and Russia found unappealing. But to frame the Communiqué falling through as solely the fault of the US and UK is misleading.
