Reform UK is in danger of looking like a “repository for disgruntled former Conservatives” if Tory defectors keep joining its ranks, Sir James Cleverly has warned Nigel Farage’s party. The former foreign and home secretary’s comments came in the wake of the defection of former Conservative chairman Sir Jake Berry to Reform.

The senior Conservative urged his party not to be “despondent” as it trails both Labour and Reform in the opinion polls a year after its devastating election defeat. He compared the Conservatives to ancient Romans after they suffered calamitous losses to Hannibal’s forces at the Battle of Cannae in 216BC.

He said Reform will now be judged on how well it can run schools and bin collections in the councils it controls and pledged the Conservatives will “fight back”.

Taking aim at Mr Farage’s party – whose MPs include former Conservative MP Lee Anderson and former Conservative councillor Sarah Pochin – he said: “If their sales pitch is ‘we are not like the old political parties’ but they are mainly populated with people from my political party, it’s going to be really hard for them to reconcile that sales pitch – so what are they? Are they new, are they different, are they exciting, or are they a repository for disgruntled former Conservatives?”

He warned people in his own party against defecting, saying it is “unsurprising” that “politically ambitious” politicians choose to “the party which is riding high in the polls”.

Sir James said former Conservatives “lose credibility” if they say: “The thing that made me realise I wasn’t really a Tory was being booted out of office by the electorate.”

Arguing that Reform will suffer a backlash if it fails to deliver for voters living in Reform-controlled council areas, he said: “This is the bit of government that runs their adult social care, their roads, their schools, their waste collection. And when governments get stuff like that wrong, people notice and people respond.”

Urging fellow Tories not to lose heart, he said: “There is no point in being despondent and there is definitely no point in being fatalistic about this.

“The prediction of the demise of the Conservative Party [has happened] a number of times before, and we are the oldest and most successful political movement in human history for a reason – we adapt, we evolve, we fight back.”

Looking back at his own experiences, he said: “Just before I became chairman of the Conservative Party, we had our worst-ever result in the European Parliament elections. In a national election, we had less than 10% of the vote and we then went on to win the 2019 General Election with one of the largest majorities in recent years. So, change happens and change happens fast.”

He also warned against attempts to change the leader.

Sir James said he told people in the wake of his lost leadership bid last year: “We have got to get out of this habit of cycling through leaders in the hope that ditching this one and picking a new one will make life easy for us.”

He said Tory leader Kemi Badenoch has been “really successful” in forcing the Government to U-turn on issues such as a grooming gangs inquiry and on winter fuel payments, adding: “I think she is going to get a win hopefully on farming tax.”

The former cabinet minister also struck a cautious note on pulling out of the European Convention on Human Rights, saying: “Other signatories to the ECHR are kicking out foreign criminals much more than we are. And other countries that are not signatories to the ECHR are also struggling.

“So, I am not convinced the ECHR is on its own a silver bullet, particularly if we don’t do something about what I worry is political activism in the legal system which is trying to rewrite British border and immigration policy through case law rather than through parliamentary law.”

He also took aim at the idea that a populist government could “smash the system” and replace today’s Civil Service.

Sir James said this was the equivalent of a Formula One team telling a driver mid-race: “We’re going to smash the car to pieces and we’re going to redesign a fundamentally different car.”

Reform has been invited to comment.