Labour is planning to rule out bringing back free movement with Europe if it wins the next election.
Keir Starmer is expected to confirm that a Labour government would not go back to allowing citizens of EU member states to live and work freely in the UK.
However, he faces pressure from some of his own MPs to forge a closer relationship with Brussels, although he has ruled out rejoining the EU.
Brexit caused a schism in the Labour party with the majority of MPs and members campaigning to remain, while many Labour voters in key target seats voted to Leave.
Mr Starmer promised Labour members he would “defend free movement as we leave the EU” when he was elected leader.
But he is now focused on winning back voters the party lost to the Conservatives at the last election.
Senior Labour sources told the Mirror that Mr Starmer is planning to be "bolder" in coming weeks about why Boris Johnson's Brexit deal isn't delivering.
They claimed the party leader wanted to highlight the Government's failure to deliver on their promises at the EU referendum.
Mr Johnson has been mired in a row over tearing up border rules in Northern Ireland which Brussels claims would break international law.
But despite promising to 'take back control' with Brexit it has done little to boost sluggish growth, soaring inflation and the risk of a recession.
One Labour source said: "You can expect Keir to be bolder talking about why the Brexit deal isn't working. We don't think anybody is feeling any Brexit benefits".
He and shadow chancellor Rachel Reeves will spend the summer focusing on the economy, with speeches and visits to marginal seats.
This will include "making it very clear where we stand" on all of the big policy issues - including Brexit.
Party insiders believe they need to explain how their two big economic policies so far - 'buy, make and sell British' and a £28bn climate package - will impact on people's lives.
A Labour source said: "We recognise that people need to know where we stand on these. We're not naive. We know we haven't been heard".
It follows claims that Mr Starmer urged Labour frontbenchers to get leadership campaigns ready in case he is forced to resign over Beergate.
The Labour leader was said to have told Wes Streeting and Lisa Nandy, two leading politicians tipped to replace him, they should prepare bids for the top job.
Ms Nandy has denied the claims.