Bloomberg reports on the matter
The report here says that the European Union has yet to discuss on how to give the UK assurances over how the Brexit backstop will be used, citing an EU official. The official also said that after leaders discuss the matter tomorrow, it's unlikely that a form of words will be found before Christmas.
Do take note that the UK parliament enters into a recess period from 20 December to 7 January next year and European officials are likely to observe a similar break starting from next week as well. That means if Theresa May (should she win) or a new prime minister (if and when appointed) wants to move forward with this case and the current Brexit deal, we'll have to wait until mid-January for further developments.
