(CNN) Before Thursday, the process for triggering Brexit was a lot more straightforward.

But the High Court's bombshell ruling means Prime Minister Theresa May's government cannot begin the formal process of taking the UK out of the European Union until it gets the approval of parliament.

The government has vowed to appeal the ruling and the Supreme Court is likely to hear the case in early December.

If that bid is unsuccessful, here's how Britain's exit from Europe could be slowed down.

Firstly, MPs need to approve a new bill...

The government must draft a Brexit bill for parliament to vote on -- and the process could take anywhere from a few weeks to much longer.

Once a bill is drafted it will be presented to the Members of Parliament in the House of Commons for a first read-through and a debate.

Then there will be a second reading, more debating, and the draft will be handed to smaller sub-committee of MPs for more scrutiny.

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"The committee will then go through the bill line by line, suggesting, debating, and voting on amendments," former Scottish Labour Party MP and Leave campaigner Tom Harris explained to CNN.

"That process could take around three or four months. But politically, I doubt they'll want it to take too long."

Next there will be a third reading, yet more debating, and if everyone is happy, the bill will be passed to the House of Lords -- where the process starts all over again.

...then the House of Lords have to give it the OK

The House of Lords has similar process of going through a bill to the House of Commons. However there will be no sub-committee, and unlike MPs, Lords are not elected by the public.

"The Lords have no accountability to constituents at all, which is both a strength and a weakness," said Harris.

The Lords have no accountability to constituents at all, which is both a strength and a weakness Tom Harris

"In this case, they will need to decide whether to honor the will of the British people in the referendum -- and I suspect they will."

If the Lords make any amendments to the bill, it will then head back to the House of Commons -- adding more time to the process.

What about the politicians who backed Remain?

Added to this potential game of ping pong between the two houses are the MPs who campaigned to remain in the EU.

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While it's unlikely that enough MPs will vote against triggering Article 50 to stop Brexit altogether, there may be lengthy wrangling over a bill that pleases everyone, said Matthew Goodwin, professor of politics and international relations at the University of Kent.

"There could potentially be further delays, particularly as Labour, the Scottish National Party, and Liberal Democrat MPs are demanding more detail on the proposed Brexit deal," he told CNN.

"Though overall, 421 seats in England and Wales voted for Brexit, so for MPs to push against the popular vote would be political suicide. "

Then there's the Scottish MPs to consider.

Other legal cases

Thursday's case was brought to the High Court by investment manager Gina Miller and hairdresser Deir dos Santos in an attempt to "uphold the highest standards of transparency and democratic accountability."

Could it also pave the way for more successful cases against the government?

Harris says that while more legal challenges could arise, it's unlikely the courts would rule in favor of them.

"I think now it makes it more difficult for individual legal cases to succeed, because the courts would have taken the view that parliament has already been given a say on the matter," said Harris.

"So in that respect, perhaps the high court has even done the government a favor."

Whether May agrees with him, is another matter.