Alan Kettley, chairman of the European Banking Federation's European Monetary Union committee, said: 'We don't know if it could be done in five years from the time a decision is made on a single currency. People are only beginning to realise the problems involved.'
Mr Kettley is conducting a survey among banks on economic and monetary union which covers the practical issues of a single currency.
He said that as with Britain's switch to a decimal currency in 1971, banks would be crucial in the smooth change to a single currency if and when the political decision was made.
However, the Maastricht treaty timetable of EMU by 1999 was not realistic, Mr Kettley said.
'We plan to have information from the survey at the end of the year,' he said. The five-year minimum adaptation view was shared by most European banks.
The choices are a 'Big Bang' approach or temporarily operating national currencies alongside the European unit during a period of adaptation.