MADRID (Reuters) - Spanish banks Santander (>> Banco Santander, S.A.) and Caixabank (>> CaixaBank SA) and HSBC Holdings Plc (>> HSBC Holdings plc) have declared a 20.3 percent stake in Spanish media group and highly indebted owner of El Pais newspaper Prisa (>> Promotora de Informaciones S.A.) through debt-for-share swaps.

According to data updated on the stock exchange web site on Wednesday, banks, also including UBS (>> UBS AG) and Morgan Stanley (>> Morgan Stanley), held a total of 28 percent of the company.

The move follows a period of upheaval at Spanish media companies, three of which have changed editors in recent months amid financial difficulties due to shrinking advertising revenue.

The stakes will be diluted on the back of a 100 million euro ($134 million) share issue to be taken up by Mexican businessman Roberto Alcantara, who said on July 22 he was buying a 9.3 percent stake in the media firm.

($1 = 0.7475 Euros)

(Reporting by Robert Hetz; Writing by Paul Day, editing by David Evans)