Barclays is moving £166bn (€190bn) of assets to Dublin because it "cannot wait any longer" to implement its Brexit contingency plan.
The high court approved the lender's Brexit contingency plans that include transferring the assets linked to about 5,000 of its clients to a Dublin-based unit.
Details of the move were revealed in a judgment by Mr Justice Snowden that largely approved the "huge" transfer, which will apply to thousands of clients of the bank. It said: "Due to the continuing uncertainty over whether there might be a no-deal Brexit, the Barclays group has determined that it cannot wait any longer to implement the scheme."
"Barclays will use our existing licensed EU-based bank subsidiary to continue to serve our clients within the EU beyond 29 March 2019 regardless of the outcome of Brexit,” the bank said. “Our preparations are well advanced and we expect to be fully operational by 29 March 2019."
The judge added: "On any view, the scale of the transfer of business... is huge.
The bank had to ask the High Court for approval to transfer the business which took place in branches in Germany, France, Spain, Italy, the Netherlands, Portugal and Sweden for corporate banking, investment banking and some wealthy private clients.
"Barclays will use our existing licensed EU-based bank subsidiary to continue to serve our clients within the EU beyond 29 March 2019 regardless of the outcome of Brexit," the bank said. "Our preparations are well advanced and we expect to be fully operational by 29 March 2019."
The BBC reported that the number of staff at Barclays' Dublin branch is predicted to double to 300, while few jobs in London are expected to be impacted.
It is the latest instance of a bank moving business out of the UK to prepare for a no-deal Brexit as London's loss is Europe's gain. HSBC is moving assets to its French unit in Paris, while RBS has applied for a German banking license and Lloyds is setting up European subsidiaries in Berlin, Frankfurt and Luxembourg. Most of the large US banks with operations in the City are also shifting assets and staff to other EU countries.
A no-deal Brexit would leave banks without a replacement for EU passporting rights, which currently allow firms to do cross-border business throughout the bloc.
Theresa May wants to renegotiate the Brexit deal with Brussels by introducing changes to the backstop. However, Brussels is not keen to reopen discussions.