Shaggy Sheep Driver,
Not just the one engine. 25 Nene I and 30 Derwent V engines were sold to the Soviets.
Jet Aero-Engines (Russia) (Hansard, 21 February 1949)
Mr. Donner asked the Minister of Supply what types of jet engine were included among the 55 sold to the Union of Soviet Socialist Republics in 1947; what were the numbers of each; and why the licences permitting such sales were issued by him.
Mr. G. R. Strauss Twenty-five Rolls-Royce "Nene I" and 30 "Derwent V" engines were sold to Russia. In answer to the second part of the Question, I would refer the hon. Member to the reply given to him by my hon. Friend the Parliamentary Secretary on 6th December last.
The US was able to gain access to the Soviet engine copies and developments from 1951 onwards via MiG-15 wreckage in Korea. The first evaluations on intact airframes were from two Polish defections to Denmark in 1953. These aircraft were returned. Later in 1953 the US got to keep and evaluate a MiG-15 after a North Korean Pilot defected.
Details from the history of the US National Air and Space Intelligence Center (NASIC)
http://www.nasicaa.org/chapter02.pdf
The US evaluated the RD-500 (Derwent V) powered Yak-23 Flora during 1953.