https://www.bbc.com/news/uk-politics-46509288
"Prime Minister Theresa May has called off Tuesday's crucial vote on her Brexit deal so she can go back to Brussels and ask for changes to it.
"As it stands the deal 'would be rejected by a significant margin' if MPs voted on it, she admitted."
The biggest stumbling block appears to be the issue between Ireland and Northern Ireland. In particular, what the borders will look like in terms of what people and goods will need to do or not do in order to cross it.
(Score: 1, Insightful) by Anonymous Coward on Wednesday December 12 2018, @10:01PM
Yeah, the referendum gave a nice broad requirement: "leave the EU" but you can't implement a broad requirement (just think how many ways you could implement the requirement "I want a program to paint pictures" - few of them are adobe photoshop) so they need to refine it into an actual specification for what the voters want and then the steps to implement. But doing that refinement without involving the voters directly makes it very unlikely they'll end up with what they want.