European Commission (EC) president, Jean-Claude Juncker, has conceded the Brussels bureaucracy has made "major mistakes" in the past. His comments, in Russia, came a week before the UK is due to vote in its highly contentious referendum on whether it stays or exits the EU. Carmakers operating in the UK want the country to remain 'in' but the opposite view is held by other auto industry-related firms such as construction equipment maker JCB.

Polls are currently ebbing and flowing only very slightly in favour of both camps but the UK car industry has consistently backed the 'Remain' campaign, albeit with reform caveats.

"I think our British friends would be best advised not to do it [leave]," Juncker said at this week's St Petersburg International Economic Forum (SPIEF), where his own visit had caused some major disquiet given Brussels' imposition of sanctions against Russia following its annexation of Crimea.

"If Britain leaves the European Union (EU), this will open up a lot of major uncertainty. We have to face crises enough – we don't have to have another crisis. We will continue the process of closer cooperation of deepening EU economic and monetary union.

"This Euroscepticism is not only present in Britain. As a commission, we made some major mistakes in the the last decades. The less we are doing, the better we are doing, the more people will understand the EU is the only answer our continent has when facing global challenges."

Juncker did not duck the thorny question of sanctions, either, mentioned time and again by speakers in St Petersburg. He was due to meet Russian president Vladimir Putin directly after his address to discuss the punitive measures which are clearly hurting Russian trade.

"We need to have a frank conversation today," said Juncker. "The illegal annexation of Crimea puts the relationship between the EU and Russia to a severe test.

"Non-use of force and territorial integrity matter – they cannot be ignored. The EU efforts to explain are not always accepted. But it is not broken beyond repair – we must keep talking even when economic sanctions are in place.

"I have known President Putin for many years – we talk often and openly. If we need to have a frank conversation today, it will not be the first and probably not the last.

"It is true, history has often divided our peoples. Russia has an opportunity and also a duty to use its power to work along[side] the EU as our partner…it is not a utopian vision. We may disagree on many things, but we must agree on the rules.

"Our path must begin with Ukraine – everyone must respect that – Russia is party to the Minsk agreements. Therefore, the next step is clearly full implementation – no more no less.

"This is the only way to lift the sanctions."