Jeremy Corbyn has warned Boris Johnson he is not above the law after the prime minister suggested he would refuse to seek another Brexit extension despite MPs passing a bill to prevent a no deal.

Speaking on a visit to Norwich on Saturday, the Labour leader said: “We’re in quite extraordinary territory when the prime minister says he is above the law.

“They are preparing for chaos. The best thing they could do is actually make sure he abides by the decision of parliament, which has passed a new act, in order to prevent a crashing out on 31 October, and extend for three months in order for there to be sensible negotiations with the EU. Any sensible prime minister would do that.”

Legal experts have warned Johnson could face prison if he refused to abide by the bill, which was passed on Friday and is set to become law on Monday.

Lord MacDonald, the former director of public prosecutions, said if Johnson refused to request an extension he could be found in contempt of court.

“A refusal in the face of that would amount to contempt of court, which could find that person in prison,” MacDonald told Sky News. “He won’t get any cooperation, apart from the fanatics around him … the attorney general won’t sit there quietly while this happens.”

The Scottish Conservative MSP Adam Tomkins, a former law professor, said Johnson should resign rather than break the law by forcing through a no-deal Brexit.

In a series of tweets, Tomkins said Johnson had only one option if he refused to ask for an extension: resign.

“Irrespective of what we think about Brexit, or the PM, surely we can all agree on one fundamental principle: the government is bound to obey the law,” he said.

“If the law compels the PM to act in a certain way, and if the PM refuses so to act, he has only one option: to resign his ministry. It really is as simple as that.”

According to The Telegraph, Johnson wrote to the Conservative membership and suggested he would not obey any legislation that required him to ask for an extension.

“They just passed a law that would force me to beg Brussels for an extension to the Brexit deadline. This is something I will never do,” he wrote.

After a speech in Wakefield earlier this week, Johnson said he would rather be “dead in a ditch” than ask for an extension from the EU, and he has also previously said he would take Britain out of Europe, “do or die”, on October 31.

MacDonald said his suggestion Johnson could be imprisoned was “not an extreme outcome” as it was convention that individuals who would not “purge their contempt” were sent to prison.

The cross-party peer added if the prime minister was to do “something as foolish as that”, he would be on his own, “maybe accompanied by Dominic Cummings”, his adviser.

MPs voted in favour of a bill designed to prevent a no-deal Brexit earlier this week, which has been passed by the Lords and is due to become law. The legislation requires the prime minister to ask the EU for the Brexit deadline to be extended beyond October 31 if a deal is not reached with Brussels by October 19.

Johnson was defeated in the House of Commons for the third time in a week when he tried to force a general election but failed to get the two-thirds majority of the house required under the Fixed-term Parliament Act.

The so-called rebel alliance of Tory MPs, including Ken Clarke and Nicholas Soames, who voted against the government over Brexit, had the Conservative whip withdrawn, with Soames saying the party was starting to resemble a “Brexit sect”.