A constitutional lawyer says the Royal Commission of Inquiry has the power to summons ex-ministers to front for its Covid enquiry. 

It's called off its second week of hearings after Chris Hipkins, Dame Jacinda Ardern, Grant Robertson, and Ayesha Verrall declined to appear. 

It says it shouldn't diminish the inquiry - as all have privately given evidence.

Lawyer Graeme Edgeler says the Commission just needs to consider if it'll miss out on key information without a summons.

"If the answer to that was yes, then they should exercise it. They seem to think at the moment that they don't need need to have the summons, but it's something they have in their back pocket."

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