A prominent U.K. economist and former chairman of the country’s financial regulator has split with his contemporaries by declaring that immigration was a “legitimate concern” in the Brexit vote last year, which he believes is now being overlooked in the current negotiations with the EU.

“I think that the most fundamental reason why the Brexit referendum passed was immigration. And I think that was a legitimate concern and in that sense I break away from many of my metropolitan, liberal friends in believing that there was a real issue there,” Adair Turner, former Financial Services Authority chairman, told CNBC on the sidelines of the Ambrosetti Forum in Italy.

He added that the disappointing progress in Brexit talks was due to a lack of focus on this particular issue. “I don’t think they’re going all that well,” Turner said about Brexit negotiations. “I think the trouble is that the negotiating stance of the U.K. is muddled; it doesn’t simply focus on saying look we’ve got to get a greater degree of control, certainly of short-term immigration surges, we’ve got to be able to control immigration flows better and that’s all that really matters.”

As British and European officials concluded the third round of Brexit talks Thursday, it was clear that both sides have made little progress. The EU’s chief negotiator Michael Barnier said the talks had failed to generate enough substance to head into a new phase – discussing a potential trade deal – which is due in October.

“I think we’ve allowed to get (the immigration argument) wrapped up with things that don’t matter like the jurisdiction of the ECJ (European Court of Justice), which frankly is an issue people have been banging on like Bill Cash (a British politician) for years and do not matter to the vast majority of the British people,” Turner, who is now the chairman of the Institute for New Economic Thinking, said.

“There’s a lack of focus on what really matters.” Turner added that the U.K. should seek to be as close as possible to membership of the EU’s single market, where goods and services travel freely. However, he acknowledged that getting that is difficult given that to be part of the common market, EU law stipulates that there needs to be freedom of movement too.