So just to close this out. What worked for me (bearing in mind this was date only, no time) was -
{
"tabulator": {
"columns": [
{
"sorterParams": {
"format": "DD/MM/YY"
},
"title": "Date",
"field": "input_date",
"width": 100,
"sorter": "date"
}
}
]
}
}
@Christian-Me thanks for showing me the way!