The EU is making sure that May knows that there won't be changes to the deal

  • There is an agreement on the table already on Brexit
  • This deal is the best and only one possible

The fact that the EU is coming out with statements like this means that the pound is not going to get any reprieve. The reason being cited for May pulling the vote tomorrow is that so she could renegotiate things with the EU on getting a better deal. If that is why she's deciding to go through with this, then there is just no way that pulling the vote here is the right option.