The British pound has slumped to a 10-month low against the US dollar after the Yes campaign took the lead in the opinion polls for the first time.
Britain's top share index has also slipped.
Scottish voters will go to the polls on Thursday 18 September to decide whether Scotland should break away from the United Kingdom and become independent.
A Sunday Times newspaper poll has put the pro-independence YES vote ahead for the first time.
It showed 51 percent support for the YES vote, compared to 49 percent for the NO campaign.
Alex Salmond from the separatist Scottish National Party said there's a clear shift happening.
The British government is promising a range of new powers for Scotland if it chooses to stay within the United Kingdom.
UK Chancellor George Osborne said a "plan of action" would be detailed in the coming days.
Speaking on the BBC Mr Osborne said: "You will see in the next few days a plan of action to give more powers to Scotland; more tax powers, more spending powers, more powers over the welfare state.
"That will be put into effect the moment there is a 'No' vote in the referendum."
He said this would give Scotland the "best of both worlds" by avoiding what he called "the risks of separation" but having "more control over their own destiny".