GENEVA (Reuters) - Switzerland's politicians have done too little to protect the country's banks from demands for data from foreign governments, UBS <UBSG.S> Chief Executive Sergio Ermotti said in an interview published by the SonntagsZeitung newspaper on Sunday.

Since the financial crisis, cash-strapped governments around the world have clamped down on tax evasion, with authorities investigating Swiss banks in Germany, France and the United States.

But Switzerland's attempts to negotiate with other governments have not provided legal certainty or closed the book on issues of the past, Ermotti said.

"This is unacceptable and opens the door for a new offensive against Swiss banks," he told the paper, adding that the government had been too ready to hand over customer data and that it is perhaps too late to get a better deal after years of negotiations.

"On some issues, the train has left the station," he said.

Last week UBS said it had been ordered by Switzerland's tax agency to provide France with tax information and it expected other countries to file similar requests.

The request related to current and former French-domiciled clients and was based on data from 2006 and 2008, the bank said.

Switzerland's tradition of banking secrecy has helped to make it the world's biggest offshore financial center, with more than $2 trillion in foreign wealth kept with the country's banks.

In 2014 French authorities placed UBS under formal examination over whether it had helped clients to avoid tax and investigating judges ordered the bank to provide bail of 1.1 billion euros ($1.22 billion).

UBS was forced in 2009 to pay a fine of $780 million and deliver the names of more than 4,000 clients to avoid indictment, providing U.S. authorities with information that allowed them to pursue other Swiss banks.

(Reporting by Tom Miles; Editing by David Goodman)