Butler also accused the PM of “deliberately” creating a “toxic” debate around the Gender Recognition Act.
She was speaking at a Labour LBGT+ hustings in Manchester on Thursday evening, alongside fellow deputy leadership candidates Angela Rayner, Dr Rosena Allin-Khan, Richard Burgon and Ian Murray.
During a quick fire question round, the discussion turned to the Conservative party’s stance on trans rights.
Butler said: “The Tories are doing this to attack a section of the community and we cannot allow this to happen. It is a deliberate attempt to divide us.
“Every time I question them in parliament they make an excuse, and it’s not f**king good enough.”
Ian Murray added: “He cannot start a sentence and end a sentence without a lie in the middle” to which Butler replied: “We have a racist and a homophobe in number 10”.
The Prime Minister has previously to gay men as “tank-topped bum boys” and black people as “piccaninnies” with “watermelon smiles”.
Referring to Johnson’s lead adviser Dominic Cummings, Butler added: “You know people by the company they keep. It’s a deliberate attempt to roll back the hard-won rights [of LGBT+ people].”
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Butler also went on to comment on the lack of transgender MPs in Parliament.
She said: “We have always ensured that underrepresented groups are represented in parliament, but we haven’t had a trans MP elected and we should have a trans MP elected.”
Butler was recently criticised after she said ‘a child is born without sex’ during a television interview.
The MP for Brent Central and deputy leader candidate made the controversial comment while appearing on ITV’s Good Morning Britain on Monday.