Former UK Prime Minister David Cameron urged Prime Minister Andy Burnham not to seek EU reentry, saying the UK should instead aim to be the bloc’s best friend, neighbor and partner.

According to Sina Finance, citing Bloomberg, Cameron told Mishal Husain that seeking to rejoin would weaken Britain’s efforts to negotiate closer ties with the EU. He said he had been “deeply disappointed” when Britain voted to leave in 2016, but that trying to overturn voters’ decision a decade later would be wrong. The full interview is due to be released Friday.

Cameron, who led the unsuccessful campaign to remain in the EU, said a debate about rejoining would be long and painful, with no clear outcome. He resigned as prime minister after the Remain campaign lost the referendum. “I am a democrat and a believer in democracy,” he said. “We have voted to leave.”

Burnham reignited the debate in a speech at the Labour Party’s annual conference in September, saying Brexit had done more harm than good. He later said all options, including rejoining the EU, were on the table. His position has been viewed as an effort to unite the pro-European left while attracting One Nation Conservatives, some of whom supported remaining in the EU and were among Cameron’s main supporters. Cameron’s opposition has raised questions about whether Burnham can use Brexit to divide center-right voters.