Holding up the foreword to the ministerial code, written by Nicola Sturgeon, the leader of the UK Labour party said it was time for the SNP leader to “live up to those high standards” and follow the “letter and the spirit” of the code.
Speaking at a virtual press conference, both politicians expressed their dismay at the nature of the leak from the Alex Salmond inquiry on Thursday night, and said the handling of the affair by the Scottish Government had damaged the integrity of parliamentary processes.
Their comments come amid reports the inquiry has concluded the First Minister misled the committee during its inquiry.
Asked whether a breach of the ministerial code was a resigning matter, Mr Sarwar said the code was clear and that a minister was expected to resign.
He said: “A breach is a breach, and a misleading of the Parliament is a misleading of the Parliament.
"Only the First Minister herself can say or judge if she knowingly did it or unknowingly did it.
"I don’t think we should hide behind an inadvertent or knowingly kind of claim. Misleading is misleading, a breach is a breach, and I think we would expect our ministers regardless again of party or of personality to be held to the highest standards."
Sir Keir said there should be a resignation if there was a breach.
He said: “We can’t pre-judge this. We’ll have to wait for the report, but if the report suggests that the First Minister has misled Parliament and potentially breached the ministerial code then that is incredibly serious.
"The code is important, the code is explicit, and the expectation has to be if there is a breach of the code then there should be a resignation.
"The foreword to the latest edition of the ministerial code was written by Nicola Sturgeon as First Minister and she said in that foreword ‘I will lead by example in following the letter and the spirit of this code’.
"She set high standards and now she needs to live up to those high standards, but we’ll have to wait and see what the report actually says next week.”
Sir Keir also criticised the response to the leak from Ms Sturgeon, arguing she had also pre-judged the report’s conclusions by criticising the leak for being “partisan”.
He said: “By making those comments, the FM is doing the very thing that she’s accusing others of. The right thing for her to do is wait for the report and read the report, as we all will.
"To say now several days beforehand what she said about the outcome is to do exactly what she is accusing other people of doing.”
Mr Sarwar said the allegation from the First Minister could also be applied to the SNP members of the committee who “never went into that independently”.
He said it was a “very dangerous allegation” that “calls into question the very processes of our Parliament” and “every committee inquiry we’ve ever had”.
The Scottish Labour leader said Ms Sturgeon should “respect the committee’s work” and “respect the findings” when the report is published.