DANIEL LEAL-OLIVAS/AFP/Getty Images

Northern Ireland's Democratic Unionist Party have dealt another possible blow to Prime Minister Theresa May's hopes of passing her Brexit deal.

Sammy Wilson, the party's Brexit spokesman, has written that a one-year extension is preferable to May's plan -- potentially dashing the possibility of the 10 DUP MPs pushing the agreement over the line this week.

"First of all let us be clear: the Withdrawal Agreement itself means no Brexit," Wilson writes in The Telegraph. "It ensures that the EU has the legal power to prevent us ever leaving except on their draconian terms, which would include a Customs Union and adherence to EU regulations."

He also sends a message to Conservative MPs such as Jacob Rees-Mogg, who have indicated they will support May's deal to secure Brexit. "To them I say that, if the deal goes through, we have lost our right to leave the EU. If we sign up to it, we give away our right to leave to the whim and dictates of the EU. That is not Brexit."

A year-long delay is "a better strategy than volunteering to be locked into the prison of the withdrawal deal with the cell door key in the pocket of Michel Barnier," he added, referencing the EU's chief negotiator.

What this means: May has attempted to flip the DUP, which props up her minority government, to support her deal for months. To date, they have not budged -- and Wilson's column makes clear that they still won't help her pass her plan.

That means that even if May can convince all of her hardline Conservative backbenchers to fall in line -- an extremely tall and unlikely order -- she may still not have the numbers to pass her Brexit plan this week.