Former Home Secretary Priti Patel will blame “those in power and control” of the Conservative Party for their heavy local election losses in a speech later.
Ms Patel will say “errors and mistakes made by a minority in Westminster have cost [the] party dearly”.
She will be among several high-profile Tory MPs speaking to the Conservative Democratic Organisation, a new grassroots pro-Boris Johnson group.
The Tory Party said it had no comment.
In extracts of the speech, seen by the BBC, Ms Patel is highly critical of the Conservative Party’s leadership.
She is expected to say that some colleagues in Westminster “have done a better job at damaging our party” over the last year than the opposition, left-wing campaign groups and “our enemies in the media combined”.
The Conservative MP for Witham will suggest that if government leaders spent more time with the grassroots of the party “they would be more in touch with the people and with our values”.
“And perhaps if they did that, last week we would not have seen 1,000 of our friends and colleagues lose their seats in the local elections and dozens of councils fall out of Conservative control.
“Never again should the grassroots of our party be side-lined, neglected and ignored,” the former cabinet minister is expected to say.
The Conservatives lost control of 48 councils and lost more than 1,000 councillors in May’s English local elections.
Many in the party were angry at the scale of the losses, which were worse than predicted, with some blaming Prime Minister Rishi Sunak.
Ms Patel was a close ally of Mr Johnson and served as home secretary during his premiership.
She will deliver her speech at the Conservative Democratic Organisation conference in Bournemouth, which will be attended by other high-profile supporters of Mr Johnson including Jacob Rees-Mogg and Nadine Dorries.
In the speech, Ms Patel is also expected to blame the MPs who removed Mr Johnson from power, saying “they took down a vote-winning political giant”.
Voters are feeling “anger, frustration and disappointment,” she will say.
She will also criticise recent budgets for featuring “more state control, more spending, and more taxes ” and diverging from what she calls Conservative values.
She will warn that if the party does not change it will risk losing more votes.
Reacting to Ms Patel’s comments, the Liberal Democrats said the Tories had “decided to rekindle their infighting” and the party was marked by “constant chaos”.