You're being optimistic Howard by stating that 'there will be no time to go back after March 2019.'
Brexit negotiations: David Davis says 'promising start' made
http://www.bbc.co.uk/news/uk-politics-40321271
I think the opinion polls are confusing a referendum with votes ........as in Eurovision Song Contest.
The entry from EU chief negotiator Michel Barnier's entry was:
David Davis countered with:
.........we haven't come anywhere in the Eurovision contest for years and it's not likely to change anytime soon!