Najib Abdul Razak's lead counsel has demanded the government explain why it is allegedly concealing the existence of a royal supplementary order allowing the former premier to serve the rest of his jail sentence under house arrest.

Muhammad Shafee Abdullah told the media outside the Kuala Lumpur High Court this afternoon that he received no response to the letters he sent to multiple ministers seeking confirmation of the royal addendum, including Prime Minister Anwar Ibrahim.

"One cannot conceal it (royal addendum). This is the...