Allies of Ms Rayner said that she shared concerns about the plans and would be prepared to vote against them if they came before the Commons.
One said she feared they would “play into” a narrative of the state versus the people which could be exploited by opposition politicians such as Mr Farage.
They added that the former deputy prime minister had also expressed concerns that the reforms may be seen as “unjust” and eroding the right to a fair trial.
‘Us-and-them system’
Labour MPs have said the changes will create an “us-and-them system” which penalises working-class defendants and compared them to justice in Vladimir Putin’s Russia.
They issued the warning as the number of Labour backbenchers who have publicly signed a statement calling on the Government to “abandon” the proposals reached 15.
The Telegraph has been told that more than three times that number have privately committed to joining the rebellion should it be needed.
That means the growing number of rebels is getting close to threatening No 10’s Commons majority, with 84 needed to defeat the Government.
Labour MPs are privately speculating that, were the reforms to be shelved, it could cost Mr Lammy his job.
That would free up the deputy premiership for a return for Ms Rayner, with Sir Keir having stated he wants to bring her back into his Cabinet.
One Labour MP said: “They’ve upset quite a lot of people and it might end up with a difficult problem in the Commons. Even Reform are saying they’ll defend the juries.
“If Lammy was to set his cap out and then failed to deliver the reforms, he looks to me as though he could well be in trouble.”
