The Swiss bank is in the process of notifying London-based staff about the moves that will affect its main divisions, namely investment banking, wealth management and asset management, the source said.

Credit Suisse, which employs about 5,500 people in London, will grow its Madrid headcount to almost 300 after the moves, while the Spanish capital will also serve as a hub for South America where the bank wants to expand its client network.

The news, which was first reported by Spanish paper Vozpopuli, comes as slow progress in post-Brexit negotiations with Brussels has raised fears of a so-called "hard Brexit" that would cause major disruption to global banks who run their European businesses from Britain.

With an October deadline on the trading relationship between Britain and the EU, banks are losing hope that they will be able to retain "passport" access to EU financial markets and have started implementing contingency plans.

U.S. banks including Goldman Sachs and JPMorgan are looking to beef up regional offices across Europe including Paris, Madrid and Milan.

Barclays has begun shifting 40 to 50 investment banking jobs from Britain to Frankfurt, while Citigroup is boosting its operations in France ahead of Brexit with a series of senior appointments.

For Credit Suisse, Madrid will not be the only destination as it is looking to relocate staff to multiple EU locations, the source said, while adding that London will still play a role even after Brexit.

(Reporting by Pamela Barbaglia; Editing by Alexander Smith)