Yes they can. They just don't have the balls.
They do not have the political capital to do it.
Theresa may could stop Brexit today if she had the nerve. Yes, it would probably bring about the collapse of the government,
LOL its democracy she would lose the support of her party and be out of job in no time, there are already murmurings she might face a challenge this week.
but we can have a general election and get a new government. Once Brexit is done, it will take years, maybe decades to repair the damage.
What new government, the best you can hope for is a hung Parliament with the LibDems getting into a coalition and forcing another vote. Labour would do Brexit, hard to tell what they will do actually because the Marxists will want out.
The damage caused... yeah try Corbyn we will be bankrupt in fours years make Brexit insignificant.
Be honest, do you think the negotiations are going well?
The EU have offered Norway or Canada +++, if Labour were not holding the country hostage for political gain a Norway type deal would get through Parliament.
Whatever happens has to get through Parliament, no scenario you present will happen, that is political reality.