John Bercow has warned Boris Johnson against disobeying the law designed to stop a no-deal Brexit, saying Parliament would thwart that.
In a speech, the Speaker said the only possible Brexit was one backed by MPs.
A new law, passed before the suspension of Parliament, forces the PM to seek a delay until 31 January 2020, unless a deal or no-deal exit is approved by MPs by 19 October.
The PM has said he would rather be “dead in a ditch” than ask for a delay.
The law received royal assent on Monday, the final day that MPs sat in this session.
Parliament was prorogued for five weeks in the early hours of Tuesday.