Vaccines minister Nadhim Zahawi told Times Radio on Tuesday that “of course we will go to parliament for a vote” if Johnson decides to proceed with passports.
But a government update on Monday raised questions about whether a Commons vote would even be needed for business to go ahead with Covid status checks for entry, as long as they comply with equalities legislation.
The document said the government was against imposing a ban on status checks and that it was “right” for ministers to provide people with a means of demonstrating Covid status, for example through the NHS Covid phone app.
The position raises questions on what exactly MPs would be voting on when they consider domestic vaccine passports.
Commenting on the proposals, Blackford said: “The UK government hasn’t published any firm proposals on Covid certificates, and the Tory position has been mired in confusion and contradiction.
“On the basis of the information available, SNP MPs would not support Tory plans due to serious concerns over ethics.
“Depending on the global context, there might be a need to consider means to facilitate international travel.
“Any such proposals could only be agreed in full consultation with the devolved governments.
“There also remain considerable issues to resolve on equity, ethics and privacy, which the UK government has not addressed.
“This is a matter of serious concern.”
On Tuesday, the Labour briefing confirmed the party will vote against passports, which it believes are discriminatory.
But Labour left the door open to backing testing certification that could, for example, allow people to attend large events after a negative Covid test.