Duke Energy has had a difficult time dealing with investor response to its after-hours CEO change following the completion of its merger with Progress Energy.

FORBES: Duke Worth $70 On Merger Synergies, Improving Margins

The completion of the single market was set in train only in the 1980s and remains a work in progress.

ECONOMIST: Fit at 50? | The

But he said the UK should focus on three areas - completion of the single market, enlargement of the EU and trade deals with the US and other leading economies - where progress could not be achieved alone and which would make both the UK and the EU a "more effective global power".

BBC: EU exit would be 'fatal mistake' says Ken Clarke