The probe is linked to alleged tax avoidance and it isn't yet known how much money is involved.
A spokesperson for the High Court told Reuters that the police had conducted the visit on the court's instruction, seeking documents relating to a number of accounts.
A Santander spokesperson said:
The bank has received an official request for information regarding certain account transactions between banks. We are providing and will continue to provide all information as requested by authorities and will cooperate, as always, with their requests for information.
An HSBC spokeswoman in London declined to comment.
Herve Falciani, a computer specialist who worked for HSBC in Geneva, leaked data exposing details of the dealings of some of the bank's wealthy clients to French officials.
Thousands of pages of data were subsequently obtained by a collaboration of news outlets including Le Monde, the Guardian, the International Consortium of Investigative Journalists and BBC Panorama.
This resulted in allegations that HSBC's Swiss private banking unit had helped wealthy clients evade millions of pounds in tax.
Falciani himself was subsequently arrested for his actions. Most recently, last November, he was sentenced to five years in prison by a Swiss court.
At the time it happened, the data leak was one of the biggest of its kind.