Both the remain and leave lead campaigners sent a mailing to every household in the country. Those and other costs were swallowed by the taxpayer, as outlined here.
https://www.electoralcommission.org...m-on-the-uks-membership-of-the-european-union
Oh, and Leave spent around £1.2M more of our money on that than Remain did.
Bout the same difference as the vote then .