FILE PHOTO: The logo of Citibank is pictured at an exhibition hall in Bangkok, Thailand, May 12, 2016. REUTERS/Athit Perawongmetha/File Photo

MADRID (Reuters) - Citigroup C.N is at an advanced stage in plans to move part of its private banking unit from London to Madrid next year as a result of Britain's decision to leave the European Union, a source familiar with the matter said on Thursday.

Several banks are opting to build up subsidiaries outside Britain so their trading operations in the EU continue without too much disruption once Britain leaves the bloc in March 2019.

“There is an advanced plan to move part of the private banking unit to Madrid during 2018,” the source said, confirming an earlier report about such a move by Citgroup that was carried in the Spanish newspaper El Pais.

El Pais said that fewer than 50 people could be transferred, while the source said the number would be lower still and the final number and a decision would be taken as Brexit negotiations unfold.

Citigroup in Madrid declined to comment.

Madrid has been seeking to lure global banks after Brexit, but so far few have signaled that they will use the Spanish capital as a significant hub.

Details of banks’ Brexit arrangements are starting to emerge following a July 14 deadline for them to submit contingency plans to the Bank of England.

Last week, Citigroup and Deutsche Bank DBKGn.DE said they would beef up their presence in Frankfurt due to Brexit.

When Citigroup first revealed its plans on July 20 to have its main footprint in Frankfurt, the U.S. bank also said it would over time increase its presence in other key EU cities, including Amsterdam, Dublin, Madrid and Paris.