In 2014, Santander unit BZ WBK's Chief Executive Mateusz Morawiecki, now Poland's Prime Minister, was forced to abandon rebranding after criticism from KNF.

Since then, KNF management has been replaced. In 2015, the eurosceptic Law and Justice (PiS) party won a general election and changed almost all state-run institutions and company managements.

"The rebranding case was accepted by KNF taking into account Santander's investor obligations and in line with the law," a KNF spokesman said in an emailed comment to Reuters on Friday, without giving further details.

Investors are keen to know the cost of the rebranding, but the bank's press office declined to comment on Friday. Next week, BZ WBK presents its first quarter results and is expected to address questions regarding the plan.

Some analysts estimate the cost of rebranding at around 50 million zloty (10.70 million pounds).

(Reporting by Marcin Goclowski; Editing by Mark Potter)