The Royal Bank of Scotland and Lloyds Banking Group, which owns Bank of Scotland, will relocate part of their Scottish business and headquarters to England, if Scots vote for independence in one week's time.
The two banks, which are partly owned by the state, revealed in separate statements that contingency plans involve moving certain of their financial dealings to England in the event that Scotland votes for independence.
Lloyds, which is 25% government owned, said it had already devised a contingency plan if Scotland became independent, which includes setting up "new principle legal entities in England".
RBS said: "There are a number of material uncertainties arising from the Scottish referendum vote which could have a bearing on the bank's credit ratings, and the fiscal, monetary, legal and regulatory landscape to which it is subject.
"For this reason, RBS has undertaken contingency planning for the possible business implications of a 'Yes' vote. RBS believes that this is the responsible and prudent thing to do and something that its customers, staff and shareholders would expect it to do.
"As part of such contingency planning, RBS believes that it would be necessary to re-domicile the bank's holding company and its primary rated operating entity (The Royal Bank of Scotland plc) to England.
"The vote on independence is a matter for the Scottish people. Scotland has been RBS's home since 1727. RBS intends to retain a significant level of its operations and employment in Scotland to support its customers there and the activities of the whole bank."
Scottish people will vote in an independence referendum on 18 September, 2014, and will be asked the straight "yes/no" question: "Should Scotland be an independent country?"
Scotland's financial services industry generates around £7bn (€8.8bn, $11bn) to £9bn for the economy and employs around 100,000 people.
The Scottish banking industry accounts for 13% of all banking employment in the UK.
Lloyds employs 16,000 staff in Scotland while RBS employs 11,500.
Bank of Scotland has 293 bank branches while RBS has 270.
Both banks have warned of the uncertainty presented by the pro-independence campaign and have announced in financial statements that their concerns have led to them coming up with back up plans.
Ratings agency Standard & Poor's has also staunchly warned that an independent Scotland could lead to an financial system collapse like Iceland because it would be unable to credibly support its lenders.