BBC reports on the matter

Says that there's talk of a letter by Juncker/Tusk that will set out reassurances on the backstop by Monday. But the BBC is reporting that this isn't 100% confirmed.

I reckon this is what is helping to give the pound a tad bit of a lift from the lows today but take it with a pinch of salt. Any reassurances won't be enough to sway parliament unless they are going to be legally-binding, which they are definitely not going to be.