Tory leader Kemi Badenoch accused Reform UK of "copying our homework" with its immigration proposals after the rival party announced plans to seek returns agreements with countries such as Taliban-run Afghanistan.
Mrs Badenoch said the only workable parts of Nigel Farage's pledges had come from Conservative policy but that Reform was "not doing the thinking" required to deliver.
The former Tory government had planned to send some migrants on a one-way trip to Rwanda in a bid to deter small boat crossings in the Channel.
But the abandoned scheme, which Government estimates suggest cost around £700 million, became mired in legal challenges and Home Secretary Yvette Cooper has said only four people were removed from the country voluntarily.
From what Reform has announced today, they haven't done the thinking, they've just copied our homework Kemi Badenoch
Mrs Badenoch refused to say how many migrants a new Conservative administration would seek to deport when questioned about Mr Farage's ambition to remove up to 600,000 people over the course of a parliament, insisting "it's not about the numbers".
"It's not about the numbers, it is about making sure that we control our borders and we get all the people who are breaking our laws and coming here illegally out of the country," she told journalists on a visit to Chelmsford on Tuesday.
"Imitation is the sincerest form of flattery, we put out a deportation Bill in May. The stuff that actually works in what he said has come from there."
The Tory "Bill" announced earlier this year included plans to disapply the Human Rights Act from all immigration-related matters and "introducing powers to deport all foreign criminals".
Mrs Badenoch has ordered a review into whether the UK should leave the European Convention on Human Rights (ECHR), which she said would report back before the Tory party conference next month.
Asked about Mr Farage's pledge to leave the treaty, she said "saying you're going to leave the ECHR is not a plan."
She said that it will have an impact on things such as the Good Friday Agreement and needs to be done in a way that does not destabilise the country or economy.
At a press conference on Tuesday, Reform pledged to scale up detention capacity for asylum seekers to 24,000 and secure deals with countries such as Afghanistan, Eritrea and Iran to return migrants to their countries.
The Tory leader refused to say whether she would consider seeking such an agreement with Taliban-run Kabul but warned "some countries will not co-operate".
Speaking to the PA news agency, Mrs Badenoch said: "We need to make sure that anyone who comes to our country illegally is deported. We have experience in government of finding some of these deportations difficult.
"That is why we had the third country deterrent, which was the Rwanda plan. Some countries will not co-operate.
"But from what Reform has announced today, they haven't done the thinking, they've just copied our homework, but they don't understand the reasons behind them."