Statement from the Government
It would be unfair to the Scottish people to ask them to make a crucial decision on independence without the necessary information about the risks of the UK's future with the EU
That's dripping with irony as the same could be said of the Brexit referendum ;-)
May has said 'no dice' on a 2nd Scottish vote. For one thing it would open a huge can of worms for people to call a second Brexit vote. For another thing, this is all just political posturing by Sturgeon. The dates suggested put it firmly towards the end of the Brexit negotiation (why not offer a vote after the Brexit deal?).
I suspect that there's deals being made under the table that will get Sturgeon a seat somewhere near the head (but not too close) of the Brexit negotiating table, and that she'll get a 2nd ref promise for after the negotiations.
Still, May's upcoming knock-back will have her shouting from every roof top.