THE president of the Confederation of British Industry will tonight urge businesses to "turn up the volume" of their support for UK membership of the European Union, warning the choice is between "openness and isolation".

Sir Mike Rake, addressing the CBI's annual dinner in London, will say that no-one has yet set out a credible alternative future to EU membership.

He will observe that the SNP's "expected but dramatic" gains in the General Election put devolution "once again at the forefront of policy".

However, he will highlight the CBI's view that, beyond promises already made such as those in the draft Scotland Bill, "further devolution of power must be driven by economic evidence, not political expediency".

The British Bankers' Association (BBA) yesterday declared that banks had put off decisions about whether to invest in the UK until after the proposed referendum on EU membership, which Prime Minister David Cameron has promised to hold by 2017. There has been mounting speculation that the referendum could be held in 2016.

And a spokeswoman for Deutsche Bank, which employs about 9,000 people in the UK, said it had formed a working group to consider moving some operations to Germany or elsewhere in the eurozone in case of a UK exit from the EU or 'Brexit'.

Sir Mike will say tonight: "Business has increasingly spoken out on this crucial issue and the time has come to turn up the volume, speaking out clearly and in a language which people can understand.

"In the months to come, our country will have to make its own choice. A choice between openness and isolation. Between shaping the future or retreating into the past."

He will add: "The question is not whether the UK would survive outside the EU, but whether it would thrive. No-one has yet set out a credible alternative future to EU membership. The current alternatives are not realistic options - little or no influence and the obligation to comply with EU principles whilst still paying most of the costs."

Sir Mike will declare that Norway is the 10th-greatest contributor to the EU budget - in spite of not being a member. And he will note that it took Switzerland nine years to negotiate and implement partial access to the EU single market.

He will tell his audience: "Business must be crystal clear that membership is in our national interest. The EU is key to our national prosperity. Letting us set the trade agenda, be part of the biggest free trade deal ever negotiated - TTIP [the Transatlantic Trade and Investment Partnership] - and be able to properly compete with global giants like China and India."

Sir Mike will highlight his view that the "moment is ripe" for reform of the EU to make it "more competitive", while emphasising his belief that this can be achieved without treaty change.

He will also underline the economic benefits of "skilled migration" to the UK, telling his audience: ""We need to keep up-skilling our population at home and attract the best and brightest European and global talent. Many businesses - and our National Health Service - could not operate without skilled migration."

BBA chief executive Anthony Browne said yesterday: "Some banks have recently moved operations and jobs out of the UK due to punitive hikes in bank taxes. Other banks have deferred decisions about whether to invest in Britain until after the referendum.

"A prolonged period of uncertainty over the UK's membership of the EU and its access to the single market could undermine international banks who are big employers in Britain."

The BBA said that former City regulator Sir Hector Sants and management consultancy firm Oliver Wyman had agreed to lead a review, on behalf of the banking industry, into the competitiveness of the UK.