Peter Mandelson has suggested the UK could start talks on rejoining the EU in 10 years’ time, much earlier than Keir Starmer believes. Lord Mandelson told an audience in Edinburgh the “truth is that [reversing Brexit] could be a conversation which starts in 10 years’ time”, but only if EU member states were willing to consider it. He said that in the meantime it was essential for the UK’s productivity and growth to reduce the damaging impact of the Brexit deal struck by Boris Johnson “as best we possibly can”. Mandelson’s remarks, at a lecture for the thinktank Reform Scotland, are in contrast to the prime minister’s prediction before the general election that the UK would not rejoin the EU, or the single market or customs union, in his lifetime. That appeared to rule out re-entry even if Labour wins a second term but Mandelson, a former European commissioner, made it clear he believed the economic damage caused by Brexit meant the prospect of rejoining the EU remained relevant. “The very hard Brexit forced through by Boris Johnson means that we are for now driving with the economic handbrake on – we can’t let that handbrake off. It is what is,” he said during his lecture. “It is difficult to see this being reversed within the next decade. That’s not just about our politics but the politics of the European Union. We are repeating the mistakes of the Brexit economic saboteurs if we think re-entry to the EU or even renegotiation is anything like a unilateral decision on our part. It isn’t. “So the new government will have to focus in the meantime on mitigating the higher barriers we have created to our nearest and largest market as best we possibly can.” The former Labour minister said Brexit was only one of the factors that had damaged the UK’s productivity. Chronic and persistent underinvestment, particularly during the last 14 years of Conservative government, was the chief driver, he said. The UK, he added, was the only member of the G7 group of wealthy economic nations in which investment was below 20% of GDP. He said proposals by Rachel Reeves, the chancellor, to reset the UK’s borrowing rules and leverage private finance to promote much greater investment were correct. The key was to focus on the economic and social value of extra spending, not its monetary value. Asked by the Guardian whether he was suggesting talks on rejoining the EU could start in 10 years, Mandelson said he was not speculating but proceeded to sketch out scenarios where that was possible. “The truth is it could be a conversation that starts in 10 years’ time. It could be longer, but the beginning of a conversation is not the end of that; it’s not the resolution of our relationship to the European Union,” he said. “I think it’ll be very hard to persuade people in the European Union to revisit, to re-engage and start getting into another negotiation about Britain’s membership of the European Union, for a long time to come. I’m sorry to say that but they have had it up to here with us. “Now does that mean to say we can and should do nothing, of course not. We’ve got to build trust, mutual respect, we’ve got to identify areas where we can cooperate and collaborate. Defence and security is an example; we’ve got to find ways to mitigate the trade costs that we’re incurring. “[It] depends on how successfully we rebuild the foundations. It also depends what’s going on in the rest of the world; what’s going on in the rest of Europe that might actually make us converge a bit more; what happens in the United States that might bring Europe further together, quicker than we think.” If the UK did begin talks on rejoining the EU in the mid-2030s, that would be nearly 20 years since the EU referendum in 2016, or close to a generation in political terms.