Scotland would face an "enormous challenge" to produce their own currency if it became independent, according to the chair of HSBC, Douglas Flint.
He said: "Scotland would be faced with monetary policy implementation without representation - a very odd form of independence."
The three main parties at Westminster have all ruled out the Scottish Government's preferred option of a formal currency union between an independent Scotland and the rest of the UK.
The Scottish referendum vote will take place on September 18.
More top news
A public inquiry into undercover policing in England and Wales is to be formally opened today.
Lorries are being parked on the M20 again as a "heavy volume" of traffic heading for Europe led police to reintroduce emergency closures.
The world's top scientists have called for a ban on autonomous weapons and "killer robots" that can attack targets without human control.