The legal position is that changes to domestic laws can't be made by prerogative - only by our sovereign parliament. Invoking article 50, which triggers brexit, means that EU laws may be ditched (some would definitely have to be). But EU laws are enshrined in our domestic laws, so, de facto, they are our laws. That's the deal we signed up to when we became an EU member. They can be replaced or repealed only by parliament, not by prerogative. That's what the judges decided. The only way May can get the decision overturned is by persuading the Supreme Court that invoking Article 50 is a separate matter from changing EU laws. The High Court judges decided that they go hand in hand. I'm biased, but I agree with them. Cameron was not entitled to make his pre-referendum promises about Article 50, etc. To carry them out by prerogative would be to override the rule of law. Dunno about you, but I don't want our governments to be able to do that. We've spent centuries in this country restricting the rights of kings and queens, etc., to rule by edict/diktat. That's the democracy that the brexiteers moaned about like mad that we'd sacrificed by joining the EU, remember?