Labour is plotting to undo Brexit and take Britain back into the European Union by the back door, Tories warned.

Sir Keir Starmer and key ally Rachel Reeves admitted they want to renegotiate Boris Johnson’s deal if they seize power.

And a slew of their party’s candidates are hellbent on rejoining the bloc, vowing to campaign to take the UK back in.

Cabinet Minister Chris Heaton-Harris, a leading Brexiteer, said: “Labour wants to take us back to Brussels through the back door.

“They want to undo Brexit, return to freedom of movement and allow the European Court of Justice to have total jurisdiction in our country.

“While the Conservatives have a plan to take our country forward, Labour – backed up by the Liberal Democrats – have no plan and want to take us back to the arguments of the past. And make no mistake, a vote for Reform is a vote for Starmer.”

Ms Reeves said she wanted to seek closer alignment with EU rules in the chemicals and veterinary sectors, better touring rights for UK artists, and greater mutual recognition of qualifications for financial services workers.

The shadow chancellor said it was not an “exclusive” list, telling the Financial Times: “We would look to improve our trading relationship with Europe.

“I don’t think anyone voted Leave because they were not happy that chemicals regulations were the same across Europe.”

Sir Keir, who drew up plans under Jeremy Corbyn to hold a second referendum, said a renegotiated Brexit deal could remove “an inhibitor” to economic growth.

He said: “We took a decision to leave the EU, so we are not going to go back in. But we think the deal we’ve got is botched, it’s not good enough and I think many businesses would say: ‘We need something that works better for us.'”

The Labour Movement for Europe, chaired by Stella Creasy, who is seeking reelection for Walthamstow, campaigns to “secure” the UK’s future in Europe.

In a series of recordings of events by the group obtained by the Tories, candidates were heard speaking freely of their intentions.

Labour’s Camberwell and Peckham candidate Miatta Fahnbulleh on the group’s website saying she “very, very proudly and loudly Remain, and also to be talking about a pathway back to entering the European Union”.

In Watford, candidate Matt Turmaine said every candidate endorsed by Labour Movement for Europe shared a “commitment” to rejoining the EU that they would pursue if elected to Parliament.

He said it was “important that we're careful” that campaigners do not give the impression of trying to rerun 2016 adding: “We need to understand what it is that we need to do in order to be able to rectify it when we get into power.”

Jackie Jones, Ceredigion Preseli, said there was a growing rejoin movement, added: “We are going to march and march and march and knock that house down until we have rejoined.”

Meanwhile, shadow foreign secretary David Lammy and London mayor Sadiq Khan are pushing for a free movement deal for young people.

Labour’s admission on Brexit came as Rishi Sunak returned to the campaign trail after four days attending international summits.

The Prime Minister said he understands people’s frustrations but insisted all is still to play for despite the Conservative’s trailing in the polls.

He said: “There’s still two-and-a-half weeks to go in this election, I’m fighting hard for every vote because I believe we can win.

“And there’s a very clear choice at this election: it’s having your taxes cut by the Conservatives or facing significant tax rises with the Labour Party.”

Asked if he understands people’s frustrations with the Tory Party, with some voters deciding to turn to Reform UK, he replied: “Of course I understand people’s frustrations with that – I mean that’s undeniable, and I’ve been very clear that we have made progress, but there is more to go.

“But the point now is we are on the right track and this election is about the future.”

Grant Shapps earlier told Times Radio it is “possible to win the election”, but conceded it is “not the most likely outcome”, adding: “I’m a realist.”

Asked if a Tory victory is unlikely, he replied: “I think that’s the realistic position, isn’t it? I mean, I live in the real world. So, you know, let’s not try and pretend black is white.”