National Australia Bank is yet to decide where to establish a new European banking base following Britain's exit from the European Union next month.Britain is scheduled to cease its EU membership on March 29, which will complicate operational challenges for London-based banks trying to service Australian companies that conduct business in EU markets.The regulatory and operational costs of executing European business transactions through British-based banks is likely to soar after Britain abandons the EU.That prospect prompted most international providers with bases in London to develop plans to migrate all or part of their operations to other European jurisdictions.They include Commonwealth Bank and Westpac, which disclosed plans last year to open new operations in Amsterdam and Frankfurt, respectively.Both CBA and Westpac are continuing to engage with EU regulators to secure new banking licences this year.However, Banking Day understands that the NAB board is still considering several options to reorganise its European operations post Brexit.An announcement regarding the reconfiguration of NAB's European banking activities is expected in the next month."We are still considering the best option following Brexit and will continue to support our customers across Europe," a NAB spokesperson said."We haven't made any final decisions and are considering a range of options."NAB's slow response to the challenges thrown up by Brexit could open opportunities for the three other major banks to win over lucrative banking relationships NAB currently holds with Australian corporates that trade with Europe.ANZ looks the most likely threat to NAB because it already has banking licences to operate in France and Germany.Transaction banking mandates could flow ANZ's way if corporate customers find that NAB's late response to Brexit results in cross-border payments becoming unreliable and expensive."ANZ clients don't need to open any new accounts as the bank is well prepared and has banking licenses in France and Germany already," a bank spokesman said."We have local registrations and licenses for some lending, trade and markets services without a physical presence, servicing most European countries."Under this operating model ANZ is able to access non-UK EU markets to supply a range of lending, trade and markets services."The exodus of banking and insurance operations from London's financial district has gathered momentum since December last year.Research conducted by KPMG shows that Dublin, Frankfurt and Amsterdam are the most popular EU destinations for commercial and investment banks.Over the last six months Macquarie Bank, Barclays, Toronto Dominion Bank and Bank of America have been migrating staff and business functions to Dublin - while Goldman Sachs, Wells Fargo, UBS and Citigroup have been expanding their presence in Frankfurt.However, Luxembourg has emerged as the EU base of choice for international fund managers and insurers that traditionally based their European headquarters in London.Tokio Marine, AIG, Blackstone and Northern Trust have each announced plans to join the rush to Luxembourg City.KPMG has identified 51 financial services companies that are relocating business functions to Luxembourg and 40 firms moving operations to Dublin.Around 22 financial institutions were expected to migrate activities to Frankfurt.