And, asked if it was “remotely conceivable” that a second prorogation would be ordered – if the Supreme Court forces a recall of parliament – said the political situation was simply too volatile to make predictions.
“For me to sit here and imagine what might happen at end of October, I think, is idle,” Mr Buckland said.
“What I do know is that, if we are able to, we will have a Queen’s Speech in mid-October.”
But Mr Buckland, and the prime minister himself in a separate interview, suggested it is among the options being considered if the highest court in the land rules against the government.
Both also refused to commit to recalling parliament if the Supreme Court battle is lost, the justice secretary saying he would await “the precise wording of any judgement”.
Labour condemned the idea that the government might “ignore a court judgement and prorogue parliament all over again”.
“Any normal prime minister, faced with a ruling of that kind, would immediately go back to the Queen and ask for parliament to be recalled, said Shami Chakrabarti, the shadow attorney general.
“This is pretty scary stuff that is testing our constitution and our normal British sense of fair play to the limit.”
Mr Buckland, when speaking to BBC Radio 4’s Today programme, did not explain the threat to the Queen’s Speech, planned for the day MPs finally return to Westminster.
However, lawyers have suggested the Supreme Court, if it decides against the government might rule that the prorogation is “a nullity’.
That would mean that, in the eyes of the law, it never happened and parliament would pick up where it left off in July, with no new session and no Queen’s Speech.
Alternatively, the 11 justices could order the government to bring back parliament immediately, which could mean an earlier Queen’s Speech.
The case is expected to run for three days, including – extraordinarily – an appearance by John Major on Thursday, setting out why he believes Mr Johnson has broken the law.
It will mean a former Conservative prime minister publicly accusing the current occupant of the office of duplicity, taking the Tory civil war over Europe to new heights of division.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies