The BBC seems to be implying so...
Militant Tendency
But he was not the first revolutionary leader to advocate the tactic - the Labour Party had been expelling hard-left entryists since the 1920s.
British communists, inspired by the Russian Revolution, had little time for the Labour Party's belief in democratic socialism, believing revolution, and the abolition of Parliament, was the only way to free the working classes.
Trotskyist entryism did not begin to bear any real fruit until the 1970s, with the rise of the Militant Tendency.
Militant drew much of its support from young people hungry for social change and disillusioned with what they saw as Labour's watered-down version of socialism - they believed capitalism was beyond reform and the only answer was to nationalise private industry without compensation.
Mr Corbyn was never a member of Militant, although he fought against their expulsion in the 1980s.
And Momentum - the grassroots organisation set up to support Mr Corbyn - is clearly a very different beast, operating as it does in an open fashion.
Mr Watson has said he does not believe that the "vast majority" of Labour members that have joined the party are "all Trots and Bolsheviks".
But like many Labour MPs, he sees signs of entryist tactics at work, even though it is sometimes very difficult to get a handle on the allegiances and motivations of the British hard left.
What is a Trotskyist? - BBC News
The BBC really is utter tripe nowadays...