The government insisted the prorogation was constitutional, and normal procedure when a government wants to restart the parliamentary session with a new legislative agenda.
Johnson is travelling in NY for the U.N. General Assembly and hasn't commented yet on the adverse ruling.
Mr Cox said he respected the Supreme Court's decision, but launched a blistering attack on MPs for being "too cowardly" to hold an election, adding: "This Parliament is dead".
The main opposition Labour Party is now holding a conference in the city of Brighton, which will end Wednesday after its leader Jeremy Corbyn delivers his keynote speech. That bill, which became law on September 9, also compels Johnson to seek an extension until next year if Parliament doesn't OK a no-deal exit.
Defence Secretary Ben Wallace was filmed giving an explanation as to why Boris Johnson suspended parliament in Helsinki following the announcement, saying that the reality was due to the Brexit impasse and not the official reasoning. "And that is what we are working on", Johnson said.
However, a snap election requires support of two-thirds of MPs, and Johnson does not have even a simple majority in the 650-seat House of Commons.
At one end of the spectrum, the justices could say that the suspension was a political matter on which they cannot pass judgment.
The lawmakers at the House of Commons returned to work Wednesday, a day after the landmark ruling by the Supreme Court that said Johnson's prorogation - or suspension of Parliament - earlier this month was "void and of no effect".
"I have the upmost respect for our judiciary, I don't think this was the right decision", Johnson said in NY, where he was attending the U.N. General Assembly.
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But critics accused him of trying to silence MPs.
His lawyer Lord Garnier QC said the former prime minister is of the view the "inference was inescapable" that Mr Johnson's decision was "motivated by his political interest in ensuring that there was no activity in Parliament during the period leading up to the EU Council summit on October 17 and 18".
Scotland's highest civil court found the suspension was unlawful, but the High Court in England said it was not a matter for judges to intervene in.
While Mr Cruddas wished the then-new prime minister well, he denounced the system that saw him elected.
Johnson was quickly facing calls from opposition politicians for his resignation.
His opponents said he trying to stymie challenges to his promise to take Britain out of the European Union on October 31 with or without a transition agreement.
"The court is bound to conclude. that the decision to advise Her Majesty to prorogue was unlawful", Supreme Court President Brenda Hale said.
Johnson and other government ministers have maintained that Britain will exit on October 31 and will not accept any further delays, indicating that they might seek to ignore the legislation and possibly bring about further court battles.
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