Former Labour leader Neil Kinnock has likened Euroscepticism in the Conservative party to Enoch Powell "winning the argument from his grave".
Lord Kinnock said there had been a shift in political attitudes towards Europe since the first referendum on Britain's membership in 1975.
He served as a European Commissioner and vice-president of the European Commission.
Like Powell, Lord Kinnock lost a campaign for a "No" vote 40 years ago.
Powell also famously delivered the controversial "Rivers of blood" speech in 1968, attacking immigration - a move that cost him his front-bench job under Tory leader Edward Heath.
Reflecting on the current EU referendum and 'Brexit' question, Lord Kinnock told BBC Radio Wales' Sunday Supplement programme: "I was really fearful of the pull of investment and jobs towards the centre of the then Common Market and away from areas like the one that I represented, Bedwellty at that time.
"What was evident - although I didn't realise it at the time - was at that very time the European Commission was working on the establishment of regional development funding and various priorities and activities that would counteract that pull of investment and jobs towards the centre.
"As the years have passed it's become increasingly obvious, not only because of the regional development fund which obviously assists Wales substantially, but also because of investment decisions made more broadly that have made the UK the biggest receiver of international direct investment in all of the single market, bigger even than Germany.
"They are the two big changes politically and - vitally - economically that have taken place over the intervening years and radically and profoundly and I think irreversibly changed minds in Labour movement."
Lord Kinnock added: "It doesn't apply to all Tories - far from it - but there is an activist element, a zealous element and ideological element almost that's pulled that party in the other direction."
Speaking about Prime Minister David Cameron's draft plan to reform the UK's membership of the EU, particularly around migration, Lord Kinnock said David Cameron was "responsible for leading himself up this particularly dark alley".
"For instance, people don't generally know that there are no out of work benefits claimable as of right, by immigrants generally, including EU immigrants," he said.
"So what we are talking about only, is in work benefits, that's to say tax credits and anything associated with being eligible to claim a supplement to your wage.
"But by definition of course, you have to be working before you can make such a claim, by getting the focus so explicitly on this, I think there is a danger that David Cameron has given himself such a bar, especially in terms of the Conservative manifesto, that was always going to be virtually impossible to clear.
"The best he can do and I think he has probably achieved this, is arrangements which will ensure that the in-work benefits are abated substantially, without breaching laws of free movement. That's complex but doable."