Is there any research on by what date voters made their mind up about Brexit in the referendum campaign?
The largest Brexit exit poll I know of was released by Lord Ashcroft the day after the referendum. This online poll, conducted over the 21st-23rd of June (i.e. in the three days before the vote) interviewed 12369 voters. The third question asked (table 4 in the poll breakdown tables) asked "When did you finally decide how you were going to vote?". with responses of:
- 10% : On polling day/ the day I filled out my postal vote
- 8% : In the last few days
- 6% : In the last week
- 18% : In the last month
- 14% : Since the beginning of the year
- 6% : Longer ago than a year
- 37% : I have always known how I would end up voting
There are some minor differences between remain and leave, but nothing spectacular or significant.