The UK PM spokeswoman Alison Donnelly was out on the wires in the last hour, saying that May will never agree to backstop that will trap the UK in a customs union permanently.
Additional quotes:
“¢ Backstop must be temporary.
“¢ The future economic relationship needs to be in place by the end of December 2020.
“¢ Big issues remain in Brexit talks ahead of EU Summit next week.