The imprisonment of former prime minister Najib Abdul Razak will not cleanse Umno of its corruption-tainted image, said Pejuang chairperson Dr Mahathir Mohamad.

According to Mahathir, himself a former prime minister and former Umno president, corruption in Umno has cascaded down to the grassroots level.

This is the reason, he said, why the party should be completely rejected in the 15th general election (GE15).