The establishment are running scared as they did in the 1920's with the Zinoviev letter. Black propaganda is a constant against the left and this story will be one of a number they will attempt to discredit Corbyn.
While not actually believing an ounce of truth in the story, I disagree with this statement if by the establishment you mean the government.
For all the deficiencies in the Conservative party, their relatively woeful GE outcome, the impact of Brexit and numerous other policies...
... Labour under Corbyn, with it's own indecision and division, seems to be offering very little threat to power or a valid, directed alternative.