Well, NZMC took over BLMC NZ on May 1 1972, and BLMC changed its name to British Leyland U.K. Ltd from October 1 1972, so it would depend on the Mini's build date.
The old newspapers have some interesting stories, press releases, etc about BMC and BL.
https://paperspast.natlib.govt.nz/newspapers/CHP19720922.2.65
Like this from Sept 1972 in the Christchurch Press :-
British Leyland Marinas are now the second bestselling light car in Australia, and in recent months have outsold both the Holden Torana and the Datsun 1600, Leyland Australia has said. The corporation had a 7.1 per cent share of the Australian market in the three months to the end of July, compared with a 6.1 per cent share in the early part of the year.